linux/fs/fs-writeback.c
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   1// SPDX-License-Identifier: GPL-2.0-only
   2/*
   3 * fs/fs-writeback.c
   4 *
   5 * Copyright (C) 2002, Linus Torvalds.
   6 *
   7 * Contains all the functions related to writing back and waiting
   8 * upon dirty inodes against superblocks, and writing back dirty
   9 * pages against inodes.  ie: data writeback.  Writeout of the
  10 * inode itself is not handled here.
  11 *
  12 * 10Apr2002    Andrew Morton
  13 *              Split out of fs/inode.c
  14 *              Additions for address_space-based writeback
  15 */
  16
  17#include <linux/kernel.h>
  18#include <linux/export.h>
  19#include <linux/spinlock.h>
  20#include <linux/slab.h>
  21#include <linux/sched.h>
  22#include <linux/fs.h>
  23#include <linux/mm.h>
  24#include <linux/pagemap.h>
  25#include <linux/kthread.h>
  26#include <linux/writeback.h>
  27#include <linux/blkdev.h>
  28#include <linux/backing-dev.h>
  29#include <linux/tracepoint.h>
  30#include <linux/device.h>
  31#include <linux/memcontrol.h>
  32#include "internal.h"
  33
  34/*
  35 * 4MB minimal write chunk size
  36 */
  37#define MIN_WRITEBACK_PAGES     (4096UL >> (PAGE_SHIFT - 10))
  38
  39/*
  40 * Passed into wb_writeback(), essentially a subset of writeback_control
  41 */
  42struct wb_writeback_work {
  43        long nr_pages;
  44        struct super_block *sb;
  45        enum writeback_sync_modes sync_mode;
  46        unsigned int tagged_writepages:1;
  47        unsigned int for_kupdate:1;
  48        unsigned int range_cyclic:1;
  49        unsigned int for_background:1;
  50        unsigned int for_sync:1;        /* sync(2) WB_SYNC_ALL writeback */
  51        unsigned int auto_free:1;       /* free on completion */
  52        enum wb_reason reason;          /* why was writeback initiated? */
  53
  54        struct list_head list;          /* pending work list */
  55        struct wb_completion *done;     /* set if the caller waits */
  56};
  57
  58/*
  59 * If an inode is constantly having its pages dirtied, but then the
  60 * updates stop dirtytime_expire_interval seconds in the past, it's
  61 * possible for the worst case time between when an inode has its
  62 * timestamps updated and when they finally get written out to be two
  63 * dirtytime_expire_intervals.  We set the default to 12 hours (in
  64 * seconds), which means most of the time inodes will have their
  65 * timestamps written to disk after 12 hours, but in the worst case a
  66 * few inodes might not their timestamps updated for 24 hours.
  67 */
  68unsigned int dirtytime_expire_interval = 12 * 60 * 60;
  69
  70static inline struct inode *wb_inode(struct list_head *head)
  71{
  72        return list_entry(head, struct inode, i_io_list);
  73}
  74
  75/*
  76 * Include the creation of the trace points after defining the
  77 * wb_writeback_work structure and inline functions so that the definition
  78 * remains local to this file.
  79 */
  80#define CREATE_TRACE_POINTS
  81#include <trace/events/writeback.h>
  82
  83EXPORT_TRACEPOINT_SYMBOL_GPL(wbc_writepage);
  84
  85static bool wb_io_lists_populated(struct bdi_writeback *wb)
  86{
  87        if (wb_has_dirty_io(wb)) {
  88                return false;
  89        } else {
  90                set_bit(WB_has_dirty_io, &wb->state);
  91                WARN_ON_ONCE(!wb->avg_write_bandwidth);
  92                atomic_long_add(wb->avg_write_bandwidth,
  93                                &wb->bdi->tot_write_bandwidth);
  94                return true;
  95        }
  96}
  97
  98static void wb_io_lists_depopulated(struct bdi_writeback *wb)
  99{
 100        if (wb_has_dirty_io(wb) && list_empty(&wb->b_dirty) &&
 101            list_empty(&wb->b_io) && list_empty(&wb->b_more_io)) {
 102                clear_bit(WB_has_dirty_io, &wb->state);
 103                WARN_ON_ONCE(atomic_long_sub_return(wb->avg_write_bandwidth,
 104                                        &wb->bdi->tot_write_bandwidth) < 0);
 105        }
 106}
 107
 108/**
 109 * inode_io_list_move_locked - move an inode onto a bdi_writeback IO list
 110 * @inode: inode to be moved
 111 * @wb: target bdi_writeback
 112 * @head: one of @wb->b_{dirty|io|more_io|dirty_time}
 113 *
 114 * Move @inode->i_io_list to @list of @wb and set %WB_has_dirty_io.
 115 * Returns %true if @inode is the first occupant of the !dirty_time IO
 116 * lists; otherwise, %false.
 117 */
 118static bool inode_io_list_move_locked(struct inode *inode,
 119                                      struct bdi_writeback *wb,
 120                                      struct list_head *head)
 121{
 122        assert_spin_locked(&wb->list_lock);
 123
 124        list_move(&inode->i_io_list, head);
 125
 126        /* dirty_time doesn't count as dirty_io until expiration */
 127        if (head != &wb->b_dirty_time)
 128                return wb_io_lists_populated(wb);
 129
 130        wb_io_lists_depopulated(wb);
 131        return false;
 132}
 133
 134static void wb_wakeup(struct bdi_writeback *wb)
 135{
 136        spin_lock_bh(&wb->work_lock);
 137        if (test_bit(WB_registered, &wb->state))
 138                mod_delayed_work(bdi_wq, &wb->dwork, 0);
 139        spin_unlock_bh(&wb->work_lock);
 140}
 141
 142static void finish_writeback_work(struct bdi_writeback *wb,
 143                                  struct wb_writeback_work *work)
 144{
 145        struct wb_completion *done = work->done;
 146
 147        if (work->auto_free)
 148                kfree(work);
 149        if (done) {
 150                wait_queue_head_t *waitq = done->waitq;
 151
 152                /* @done can't be accessed after the following dec */
 153                if (atomic_dec_and_test(&done->cnt))
 154                        wake_up_all(waitq);
 155        }
 156}
 157
 158static void wb_queue_work(struct bdi_writeback *wb,
 159                          struct wb_writeback_work *work)
 160{
 161        trace_writeback_queue(wb, work);
 162
 163        if (work->done)
 164                atomic_inc(&work->done->cnt);
 165
 166        spin_lock_bh(&wb->work_lock);
 167
 168        if (test_bit(WB_registered, &wb->state)) {
 169                list_add_tail(&work->list, &wb->work_list);
 170                mod_delayed_work(bdi_wq, &wb->dwork, 0);
 171        } else
 172                finish_writeback_work(wb, work);
 173
 174        spin_unlock_bh(&wb->work_lock);
 175}
 176
 177/**
 178 * wb_wait_for_completion - wait for completion of bdi_writeback_works
 179 * @done: target wb_completion
 180 *
 181 * Wait for one or more work items issued to @bdi with their ->done field
 182 * set to @done, which should have been initialized with
 183 * DEFINE_WB_COMPLETION().  This function returns after all such work items
 184 * are completed.  Work items which are waited upon aren't freed
 185 * automatically on completion.
 186 */
 187void wb_wait_for_completion(struct wb_completion *done)
 188{
 189        atomic_dec(&done->cnt);         /* put down the initial count */
 190        wait_event(*done->waitq, !atomic_read(&done->cnt));
 191}
 192
 193#ifdef CONFIG_CGROUP_WRITEBACK
 194
 195/*
 196 * Parameters for foreign inode detection, see wbc_detach_inode() to see
 197 * how they're used.
 198 *
 199 * These paramters are inherently heuristical as the detection target
 200 * itself is fuzzy.  All we want to do is detaching an inode from the
 201 * current owner if it's being written to by some other cgroups too much.
 202 *
 203 * The current cgroup writeback is built on the assumption that multiple
 204 * cgroups writing to the same inode concurrently is very rare and a mode
 205 * of operation which isn't well supported.  As such, the goal is not
 206 * taking too long when a different cgroup takes over an inode while
 207 * avoiding too aggressive flip-flops from occasional foreign writes.
 208 *
 209 * We record, very roughly, 2s worth of IO time history and if more than
 210 * half of that is foreign, trigger the switch.  The recording is quantized
 211 * to 16 slots.  To avoid tiny writes from swinging the decision too much,
 212 * writes smaller than 1/8 of avg size are ignored.
 213 */
 214#define WB_FRN_TIME_SHIFT       13      /* 1s = 2^13, upto 8 secs w/ 16bit */
 215#define WB_FRN_TIME_AVG_SHIFT   3       /* avg = avg * 7/8 + new * 1/8 */
 216#define WB_FRN_TIME_CUT_DIV     8       /* ignore rounds < avg / 8 */
 217#define WB_FRN_TIME_PERIOD      (2 * (1 << WB_FRN_TIME_SHIFT))  /* 2s */
 218
 219#define WB_FRN_HIST_SLOTS       16      /* inode->i_wb_frn_history is 16bit */
 220#define WB_FRN_HIST_UNIT        (WB_FRN_TIME_PERIOD / WB_FRN_HIST_SLOTS)
 221                                        /* each slot's duration is 2s / 16 */
 222#define WB_FRN_HIST_THR_SLOTS   (WB_FRN_HIST_SLOTS / 2)
 223                                        /* if foreign slots >= 8, switch */
 224#define WB_FRN_HIST_MAX_SLOTS   (WB_FRN_HIST_THR_SLOTS / 2 + 1)
 225                                        /* one round can affect upto 5 slots */
 226#define WB_FRN_MAX_IN_FLIGHT    1024    /* don't queue too many concurrently */
 227
 228/*
 229 * Maximum inodes per isw.  A specific value has been chosen to make
 230 * struct inode_switch_wbs_context fit into 1024 bytes kmalloc.
 231 */
 232#define WB_MAX_INODES_PER_ISW  ((1024UL - sizeof(struct inode_switch_wbs_context)) \
 233                                / sizeof(struct inode *))
 234
 235static atomic_t isw_nr_in_flight = ATOMIC_INIT(0);
 236static struct workqueue_struct *isw_wq;
 237
 238void __inode_attach_wb(struct inode *inode, struct page *page)
 239{
 240        struct backing_dev_info *bdi = inode_to_bdi(inode);
 241        struct bdi_writeback *wb = NULL;
 242
 243        if (inode_cgwb_enabled(inode)) {
 244                struct cgroup_subsys_state *memcg_css;
 245
 246                if (page) {
 247                        memcg_css = mem_cgroup_css_from_page(page);
 248                        wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
 249                } else {
 250                        /* must pin memcg_css, see wb_get_create() */
 251                        memcg_css = task_get_css(current, memory_cgrp_id);
 252                        wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
 253                        css_put(memcg_css);
 254                }
 255        }
 256
 257        if (!wb)
 258                wb = &bdi->wb;
 259
 260        /*
 261         * There may be multiple instances of this function racing to
 262         * update the same inode.  Use cmpxchg() to tell the winner.
 263         */
 264        if (unlikely(cmpxchg(&inode->i_wb, NULL, wb)))
 265                wb_put(wb);
 266}
 267EXPORT_SYMBOL_GPL(__inode_attach_wb);
 268
 269/**
 270 * inode_cgwb_move_to_attached - put the inode onto wb->b_attached list
 271 * @inode: inode of interest with i_lock held
 272 * @wb: target bdi_writeback
 273 *
 274 * Remove the inode from wb's io lists and if necessarily put onto b_attached
 275 * list.  Only inodes attached to cgwb's are kept on this list.
 276 */
 277static void inode_cgwb_move_to_attached(struct inode *inode,
 278                                        struct bdi_writeback *wb)
 279{
 280        assert_spin_locked(&wb->list_lock);
 281        assert_spin_locked(&inode->i_lock);
 282
 283        inode->i_state &= ~I_SYNC_QUEUED;
 284        if (wb != &wb->bdi->wb)
 285                list_move(&inode->i_io_list, &wb->b_attached);
 286        else
 287                list_del_init(&inode->i_io_list);
 288        wb_io_lists_depopulated(wb);
 289}
 290
 291/**
 292 * locked_inode_to_wb_and_lock_list - determine a locked inode's wb and lock it
 293 * @inode: inode of interest with i_lock held
 294 *
 295 * Returns @inode's wb with its list_lock held.  @inode->i_lock must be
 296 * held on entry and is released on return.  The returned wb is guaranteed
 297 * to stay @inode's associated wb until its list_lock is released.
 298 */
 299static struct bdi_writeback *
 300locked_inode_to_wb_and_lock_list(struct inode *inode)
 301        __releases(&inode->i_lock)
 302        __acquires(&wb->list_lock)
 303{
 304        while (true) {
 305                struct bdi_writeback *wb = inode_to_wb(inode);
 306
 307                /*
 308                 * inode_to_wb() association is protected by both
 309                 * @inode->i_lock and @wb->list_lock but list_lock nests
 310                 * outside i_lock.  Drop i_lock and verify that the
 311                 * association hasn't changed after acquiring list_lock.
 312                 */
 313                wb_get(wb);
 314                spin_unlock(&inode->i_lock);
 315                spin_lock(&wb->list_lock);
 316
 317                /* i_wb may have changed inbetween, can't use inode_to_wb() */
 318                if (likely(wb == inode->i_wb)) {
 319                        wb_put(wb);     /* @inode already has ref */
 320                        return wb;
 321                }
 322
 323                spin_unlock(&wb->list_lock);
 324                wb_put(wb);
 325                cpu_relax();
 326                spin_lock(&inode->i_lock);
 327        }
 328}
 329
 330/**
 331 * inode_to_wb_and_lock_list - determine an inode's wb and lock it
 332 * @inode: inode of interest
 333 *
 334 * Same as locked_inode_to_wb_and_lock_list() but @inode->i_lock isn't held
 335 * on entry.
 336 */
 337static struct bdi_writeback *inode_to_wb_and_lock_list(struct inode *inode)
 338        __acquires(&wb->list_lock)
 339{
 340        spin_lock(&inode->i_lock);
 341        return locked_inode_to_wb_and_lock_list(inode);
 342}
 343
 344struct inode_switch_wbs_context {
 345        struct rcu_work         work;
 346
 347        /*
 348         * Multiple inodes can be switched at once.  The switching procedure
 349         * consists of two parts, separated by a RCU grace period.  To make
 350         * sure that the second part is executed for each inode gone through
 351         * the first part, all inode pointers are placed into a NULL-terminated
 352         * array embedded into struct inode_switch_wbs_context.  Otherwise
 353         * an inode could be left in a non-consistent state.
 354         */
 355        struct bdi_writeback    *new_wb;
 356        struct inode            *inodes[];
 357};
 358
 359static void bdi_down_write_wb_switch_rwsem(struct backing_dev_info *bdi)
 360{
 361        down_write(&bdi->wb_switch_rwsem);
 362}
 363
 364static void bdi_up_write_wb_switch_rwsem(struct backing_dev_info *bdi)
 365{
 366        up_write(&bdi->wb_switch_rwsem);
 367}
 368
 369static bool inode_do_switch_wbs(struct inode *inode,
 370                                struct bdi_writeback *old_wb,
 371                                struct bdi_writeback *new_wb)
 372{
 373        struct address_space *mapping = inode->i_mapping;
 374        XA_STATE(xas, &mapping->i_pages, 0);
 375        struct page *page;
 376        bool switched = false;
 377
 378        spin_lock(&inode->i_lock);
 379        xa_lock_irq(&mapping->i_pages);
 380
 381        /*
 382         * Once I_FREEING or I_WILL_FREE are visible under i_lock, the eviction
 383         * path owns the inode and we shouldn't modify ->i_io_list.
 384         */
 385        if (unlikely(inode->i_state & (I_FREEING | I_WILL_FREE)))
 386                goto skip_switch;
 387
 388        trace_inode_switch_wbs(inode, old_wb, new_wb);
 389
 390        /*
 391         * Count and transfer stats.  Note that PAGECACHE_TAG_DIRTY points
 392         * to possibly dirty pages while PAGECACHE_TAG_WRITEBACK points to
 393         * pages actually under writeback.
 394         */
 395        xas_for_each_marked(&xas, page, ULONG_MAX, PAGECACHE_TAG_DIRTY) {
 396                if (PageDirty(page)) {
 397                        dec_wb_stat(old_wb, WB_RECLAIMABLE);
 398                        inc_wb_stat(new_wb, WB_RECLAIMABLE);
 399                }
 400        }
 401
 402        xas_set(&xas, 0);
 403        xas_for_each_marked(&xas, page, ULONG_MAX, PAGECACHE_TAG_WRITEBACK) {
 404                WARN_ON_ONCE(!PageWriteback(page));
 405                dec_wb_stat(old_wb, WB_WRITEBACK);
 406                inc_wb_stat(new_wb, WB_WRITEBACK);
 407        }
 408
 409        wb_get(new_wb);
 410
 411        /*
 412         * Transfer to @new_wb's IO list if necessary.  If the @inode is dirty,
 413         * the specific list @inode was on is ignored and the @inode is put on
 414         * ->b_dirty which is always correct including from ->b_dirty_time.
 415         * The transfer preserves @inode->dirtied_when ordering.  If the @inode
 416         * was clean, it means it was on the b_attached list, so move it onto
 417         * the b_attached list of @new_wb.
 418         */
 419        if (!list_empty(&inode->i_io_list)) {
 420                inode->i_wb = new_wb;
 421
 422                if (inode->i_state & I_DIRTY_ALL) {
 423                        struct inode *pos;
 424
 425                        list_for_each_entry(pos, &new_wb->b_dirty, i_io_list)
 426                                if (time_after_eq(inode->dirtied_when,
 427                                                  pos->dirtied_when))
 428                                        break;
 429                        inode_io_list_move_locked(inode, new_wb,
 430                                                  pos->i_io_list.prev);
 431                } else {
 432                        inode_cgwb_move_to_attached(inode, new_wb);
 433                }
 434        } else {
 435                inode->i_wb = new_wb;
 436        }
 437
 438        /* ->i_wb_frn updates may race wbc_detach_inode() but doesn't matter */
 439        inode->i_wb_frn_winner = 0;
 440        inode->i_wb_frn_avg_time = 0;
 441        inode->i_wb_frn_history = 0;
 442        switched = true;
 443skip_switch:
 444        /*
 445         * Paired with load_acquire in unlocked_inode_to_wb_begin() and
 446         * ensures that the new wb is visible if they see !I_WB_SWITCH.
 447         */
 448        smp_store_release(&inode->i_state, inode->i_state & ~I_WB_SWITCH);
 449
 450        xa_unlock_irq(&mapping->i_pages);
 451        spin_unlock(&inode->i_lock);
 452
 453        return switched;
 454}
 455
 456static void inode_switch_wbs_work_fn(struct work_struct *work)
 457{
 458        struct inode_switch_wbs_context *isw =
 459                container_of(to_rcu_work(work), struct inode_switch_wbs_context, work);
 460        struct backing_dev_info *bdi = inode_to_bdi(isw->inodes[0]);
 461        struct bdi_writeback *old_wb = isw->inodes[0]->i_wb;
 462        struct bdi_writeback *new_wb = isw->new_wb;
 463        unsigned long nr_switched = 0;
 464        struct inode **inodep;
 465
 466        /*
 467         * If @inode switches cgwb membership while sync_inodes_sb() is
 468         * being issued, sync_inodes_sb() might miss it.  Synchronize.
 469         */
 470        down_read(&bdi->wb_switch_rwsem);
 471
 472        /*
 473         * By the time control reaches here, RCU grace period has passed
 474         * since I_WB_SWITCH assertion and all wb stat update transactions
 475         * between unlocked_inode_to_wb_begin/end() are guaranteed to be
 476         * synchronizing against the i_pages lock.
 477         *
 478         * Grabbing old_wb->list_lock, inode->i_lock and the i_pages lock
 479         * gives us exclusion against all wb related operations on @inode
 480         * including IO list manipulations and stat updates.
 481         */
 482        if (old_wb < new_wb) {
 483                spin_lock(&old_wb->list_lock);
 484                spin_lock_nested(&new_wb->list_lock, SINGLE_DEPTH_NESTING);
 485        } else {
 486                spin_lock(&new_wb->list_lock);
 487                spin_lock_nested(&old_wb->list_lock, SINGLE_DEPTH_NESTING);
 488        }
 489
 490        for (inodep = isw->inodes; *inodep; inodep++) {
 491                WARN_ON_ONCE((*inodep)->i_wb != old_wb);
 492                if (inode_do_switch_wbs(*inodep, old_wb, new_wb))
 493                        nr_switched++;
 494        }
 495
 496        spin_unlock(&new_wb->list_lock);
 497        spin_unlock(&old_wb->list_lock);
 498
 499        up_read(&bdi->wb_switch_rwsem);
 500
 501        if (nr_switched) {
 502                wb_wakeup(new_wb);
 503                wb_put_many(old_wb, nr_switched);
 504        }
 505
 506        for (inodep = isw->inodes; *inodep; inodep++)
 507                iput(*inodep);
 508        wb_put(new_wb);
 509        kfree(isw);
 510        atomic_dec(&isw_nr_in_flight);
 511}
 512
 513static bool inode_prepare_wbs_switch(struct inode *inode,
 514                                     struct bdi_writeback *new_wb)
 515{
 516        /*
 517         * Paired with smp_mb() in cgroup_writeback_umount().
 518         * isw_nr_in_flight must be increased before checking SB_ACTIVE and
 519         * grabbing an inode, otherwise isw_nr_in_flight can be observed as 0
 520         * in cgroup_writeback_umount() and the isw_wq will be not flushed.
 521         */
 522        smp_mb();
 523
 524        if (IS_DAX(inode))
 525                return false;
 526
 527        /* while holding I_WB_SWITCH, no one else can update the association */
 528        spin_lock(&inode->i_lock);
 529        if (!(inode->i_sb->s_flags & SB_ACTIVE) ||
 530            inode->i_state & (I_WB_SWITCH | I_FREEING | I_WILL_FREE) ||
 531            inode_to_wb(inode) == new_wb) {
 532                spin_unlock(&inode->i_lock);
 533                return false;
 534        }
 535        inode->i_state |= I_WB_SWITCH;
 536        __iget(inode);
 537        spin_unlock(&inode->i_lock);
 538
 539        return true;
 540}
 541
 542/**
 543 * inode_switch_wbs - change the wb association of an inode
 544 * @inode: target inode
 545 * @new_wb_id: ID of the new wb
 546 *
 547 * Switch @inode's wb association to the wb identified by @new_wb_id.  The
 548 * switching is performed asynchronously and may fail silently.
 549 */
 550static void inode_switch_wbs(struct inode *inode, int new_wb_id)
 551{
 552        struct backing_dev_info *bdi = inode_to_bdi(inode);
 553        struct cgroup_subsys_state *memcg_css;
 554        struct inode_switch_wbs_context *isw;
 555
 556        /* noop if seems to be already in progress */
 557        if (inode->i_state & I_WB_SWITCH)
 558                return;
 559
 560        /* avoid queueing a new switch if too many are already in flight */
 561        if (atomic_read(&isw_nr_in_flight) > WB_FRN_MAX_IN_FLIGHT)
 562                return;
 563
 564        isw = kzalloc(sizeof(*isw) + 2 * sizeof(struct inode *), GFP_ATOMIC);
 565        if (!isw)
 566                return;
 567
 568        atomic_inc(&isw_nr_in_flight);
 569
 570        /* find and pin the new wb */
 571        rcu_read_lock();
 572        memcg_css = css_from_id(new_wb_id, &memory_cgrp_subsys);
 573        if (memcg_css && !css_tryget(memcg_css))
 574                memcg_css = NULL;
 575        rcu_read_unlock();
 576        if (!memcg_css)
 577                goto out_free;
 578
 579        isw->new_wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
 580        css_put(memcg_css);
 581        if (!isw->new_wb)
 582                goto out_free;
 583
 584        if (!inode_prepare_wbs_switch(inode, isw->new_wb))
 585                goto out_free;
 586
 587        isw->inodes[0] = inode;
 588
 589        /*
 590         * In addition to synchronizing among switchers, I_WB_SWITCH tells
 591         * the RCU protected stat update paths to grab the i_page
 592         * lock so that stat transfer can synchronize against them.
 593         * Let's continue after I_WB_SWITCH is guaranteed to be visible.
 594         */
 595        INIT_RCU_WORK(&isw->work, inode_switch_wbs_work_fn);
 596        queue_rcu_work(isw_wq, &isw->work);
 597        return;
 598
 599out_free:
 600        atomic_dec(&isw_nr_in_flight);
 601        if (isw->new_wb)
 602                wb_put(isw->new_wb);
 603        kfree(isw);
 604}
 605
 606/**
 607 * cleanup_offline_cgwb - detach associated inodes
 608 * @wb: target wb
 609 *
 610 * Switch all inodes attached to @wb to a nearest living ancestor's wb in order
 611 * to eventually release the dying @wb.  Returns %true if not all inodes were
 612 * switched and the function has to be restarted.
 613 */
 614bool cleanup_offline_cgwb(struct bdi_writeback *wb)
 615{
 616        struct cgroup_subsys_state *memcg_css;
 617        struct inode_switch_wbs_context *isw;
 618        struct inode *inode;
 619        int nr;
 620        bool restart = false;
 621
 622        isw = kzalloc(sizeof(*isw) + WB_MAX_INODES_PER_ISW *
 623                      sizeof(struct inode *), GFP_KERNEL);
 624        if (!isw)
 625                return restart;
 626
 627        atomic_inc(&isw_nr_in_flight);
 628
 629        for (memcg_css = wb->memcg_css->parent; memcg_css;
 630             memcg_css = memcg_css->parent) {
 631                isw->new_wb = wb_get_create(wb->bdi, memcg_css, GFP_KERNEL);
 632                if (isw->new_wb)
 633                        break;
 634        }
 635        if (unlikely(!isw->new_wb))
 636                isw->new_wb = &wb->bdi->wb; /* wb_get() is noop for bdi's wb */
 637
 638        nr = 0;
 639        spin_lock(&wb->list_lock);
 640        list_for_each_entry(inode, &wb->b_attached, i_io_list) {
 641                if (!inode_prepare_wbs_switch(inode, isw->new_wb))
 642                        continue;
 643
 644                isw->inodes[nr++] = inode;
 645
 646                if (nr >= WB_MAX_INODES_PER_ISW - 1) {
 647                        restart = true;
 648                        break;
 649                }
 650        }
 651        spin_unlock(&wb->list_lock);
 652
 653        /* no attached inodes? bail out */
 654        if (nr == 0) {
 655                atomic_dec(&isw_nr_in_flight);
 656                wb_put(isw->new_wb);
 657                kfree(isw);
 658                return restart;
 659        }
 660
 661        /*
 662         * In addition to synchronizing among switchers, I_WB_SWITCH tells
 663         * the RCU protected stat update paths to grab the i_page
 664         * lock so that stat transfer can synchronize against them.
 665         * Let's continue after I_WB_SWITCH is guaranteed to be visible.
 666         */
 667        INIT_RCU_WORK(&isw->work, inode_switch_wbs_work_fn);
 668        queue_rcu_work(isw_wq, &isw->work);
 669
 670        return restart;
 671}
 672
 673/**
 674 * wbc_attach_and_unlock_inode - associate wbc with target inode and unlock it
 675 * @wbc: writeback_control of interest
 676 * @inode: target inode
 677 *
 678 * @inode is locked and about to be written back under the control of @wbc.
 679 * Record @inode's writeback context into @wbc and unlock the i_lock.  On
 680 * writeback completion, wbc_detach_inode() should be called.  This is used
 681 * to track the cgroup writeback context.
 682 */
 683void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
 684                                 struct inode *inode)
 685{
 686        if (!inode_cgwb_enabled(inode)) {
 687                spin_unlock(&inode->i_lock);
 688                return;
 689        }
 690
 691        wbc->wb = inode_to_wb(inode);
 692        wbc->inode = inode;
 693
 694        wbc->wb_id = wbc->wb->memcg_css->id;
 695        wbc->wb_lcand_id = inode->i_wb_frn_winner;
 696        wbc->wb_tcand_id = 0;
 697        wbc->wb_bytes = 0;
 698        wbc->wb_lcand_bytes = 0;
 699        wbc->wb_tcand_bytes = 0;
 700
 701        wb_get(wbc->wb);
 702        spin_unlock(&inode->i_lock);
 703
 704        /*
 705         * A dying wb indicates that either the blkcg associated with the
 706         * memcg changed or the associated memcg is dying.  In the first
 707         * case, a replacement wb should already be available and we should
 708         * refresh the wb immediately.  In the second case, trying to
 709         * refresh will keep failing.
 710         */
 711        if (unlikely(wb_dying(wbc->wb) && !css_is_dying(wbc->wb->memcg_css)))
 712                inode_switch_wbs(inode, wbc->wb_id);
 713}
 714EXPORT_SYMBOL_GPL(wbc_attach_and_unlock_inode);
 715
 716/**
 717 * wbc_detach_inode - disassociate wbc from inode and perform foreign detection
 718 * @wbc: writeback_control of the just finished writeback
 719 *
 720 * To be called after a writeback attempt of an inode finishes and undoes
 721 * wbc_attach_and_unlock_inode().  Can be called under any context.
 722 *
 723 * As concurrent write sharing of an inode is expected to be very rare and
 724 * memcg only tracks page ownership on first-use basis severely confining
 725 * the usefulness of such sharing, cgroup writeback tracks ownership
 726 * per-inode.  While the support for concurrent write sharing of an inode
 727 * is deemed unnecessary, an inode being written to by different cgroups at
 728 * different points in time is a lot more common, and, more importantly,
 729 * charging only by first-use can too readily lead to grossly incorrect
 730 * behaviors (single foreign page can lead to gigabytes of writeback to be
 731 * incorrectly attributed).
 732 *
 733 * To resolve this issue, cgroup writeback detects the majority dirtier of
 734 * an inode and transfers the ownership to it.  To avoid unnnecessary
 735 * oscillation, the detection mechanism keeps track of history and gives
 736 * out the switch verdict only if the foreign usage pattern is stable over
 737 * a certain amount of time and/or writeback attempts.
 738 *
 739 * On each writeback attempt, @wbc tries to detect the majority writer
 740 * using Boyer-Moore majority vote algorithm.  In addition to the byte
 741 * count from the majority voting, it also counts the bytes written for the
 742 * current wb and the last round's winner wb (max of last round's current
 743 * wb, the winner from two rounds ago, and the last round's majority
 744 * candidate).  Keeping track of the historical winner helps the algorithm
 745 * to semi-reliably detect the most active writer even when it's not the
 746 * absolute majority.
 747 *
 748 * Once the winner of the round is determined, whether the winner is
 749 * foreign or not and how much IO time the round consumed is recorded in
 750 * inode->i_wb_frn_history.  If the amount of recorded foreign IO time is
 751 * over a certain threshold, the switch verdict is given.
 752 */
 753void wbc_detach_inode(struct writeback_control *wbc)
 754{
 755        struct bdi_writeback *wb = wbc->wb;
 756        struct inode *inode = wbc->inode;
 757        unsigned long avg_time, max_bytes, max_time;
 758        u16 history;
 759        int max_id;
 760
 761        if (!wb)
 762                return;
 763
 764        history = inode->i_wb_frn_history;
 765        avg_time = inode->i_wb_frn_avg_time;
 766
 767        /* pick the winner of this round */
 768        if (wbc->wb_bytes >= wbc->wb_lcand_bytes &&
 769            wbc->wb_bytes >= wbc->wb_tcand_bytes) {
 770                max_id = wbc->wb_id;
 771                max_bytes = wbc->wb_bytes;
 772        } else if (wbc->wb_lcand_bytes >= wbc->wb_tcand_bytes) {
 773                max_id = wbc->wb_lcand_id;
 774                max_bytes = wbc->wb_lcand_bytes;
 775        } else {
 776                max_id = wbc->wb_tcand_id;
 777                max_bytes = wbc->wb_tcand_bytes;
 778        }
 779
 780        /*
 781         * Calculate the amount of IO time the winner consumed and fold it
 782         * into the running average kept per inode.  If the consumed IO
 783         * time is lower than avag / WB_FRN_TIME_CUT_DIV, ignore it for
 784         * deciding whether to switch or not.  This is to prevent one-off
 785         * small dirtiers from skewing the verdict.
 786         */
 787        max_time = DIV_ROUND_UP((max_bytes >> PAGE_SHIFT) << WB_FRN_TIME_SHIFT,
 788                                wb->avg_write_bandwidth);
 789        if (avg_time)
 790                avg_time += (max_time >> WB_FRN_TIME_AVG_SHIFT) -
 791                            (avg_time >> WB_FRN_TIME_AVG_SHIFT);
 792        else
 793                avg_time = max_time;    /* immediate catch up on first run */
 794
 795        if (max_time >= avg_time / WB_FRN_TIME_CUT_DIV) {
 796                int slots;
 797
 798                /*
 799                 * The switch verdict is reached if foreign wb's consume
 800                 * more than a certain proportion of IO time in a
 801                 * WB_FRN_TIME_PERIOD.  This is loosely tracked by 16 slot
 802                 * history mask where each bit represents one sixteenth of
 803                 * the period.  Determine the number of slots to shift into
 804                 * history from @max_time.
 805                 */
 806                slots = min(DIV_ROUND_UP(max_time, WB_FRN_HIST_UNIT),
 807                            (unsigned long)WB_FRN_HIST_MAX_SLOTS);
 808                history <<= slots;
 809                if (wbc->wb_id != max_id)
 810                        history |= (1U << slots) - 1;
 811
 812                if (history)
 813                        trace_inode_foreign_history(inode, wbc, history);
 814
 815                /*
 816                 * Switch if the current wb isn't the consistent winner.
 817                 * If there are multiple closely competing dirtiers, the
 818                 * inode may switch across them repeatedly over time, which
 819                 * is okay.  The main goal is avoiding keeping an inode on
 820                 * the wrong wb for an extended period of time.
 821                 */
 822                if (hweight32(history) > WB_FRN_HIST_THR_SLOTS)
 823                        inode_switch_wbs(inode, max_id);
 824        }
 825
 826        /*
 827         * Multiple instances of this function may race to update the
 828         * following fields but we don't mind occassional inaccuracies.
 829         */
 830        inode->i_wb_frn_winner = max_id;
 831        inode->i_wb_frn_avg_time = min(avg_time, (unsigned long)U16_MAX);
 832        inode->i_wb_frn_history = history;
 833
 834        wb_put(wbc->wb);
 835        wbc->wb = NULL;
 836}
 837EXPORT_SYMBOL_GPL(wbc_detach_inode);
 838
 839/**
 840 * wbc_account_cgroup_owner - account writeback to update inode cgroup ownership
 841 * @wbc: writeback_control of the writeback in progress
 842 * @page: page being written out
 843 * @bytes: number of bytes being written out
 844 *
 845 * @bytes from @page are about to written out during the writeback
 846 * controlled by @wbc.  Keep the book for foreign inode detection.  See
 847 * wbc_detach_inode().
 848 */
 849void wbc_account_cgroup_owner(struct writeback_control *wbc, struct page *page,
 850                              size_t bytes)
 851{
 852        struct cgroup_subsys_state *css;
 853        int id;
 854
 855        /*
 856         * pageout() path doesn't attach @wbc to the inode being written
 857         * out.  This is intentional as we don't want the function to block
 858         * behind a slow cgroup.  Ultimately, we want pageout() to kick off
 859         * regular writeback instead of writing things out itself.
 860         */
 861        if (!wbc->wb || wbc->no_cgroup_owner)
 862                return;
 863
 864        css = mem_cgroup_css_from_page(page);
 865        /* dead cgroups shouldn't contribute to inode ownership arbitration */
 866        if (!(css->flags & CSS_ONLINE))
 867                return;
 868
 869        id = css->id;
 870
 871        if (id == wbc->wb_id) {
 872                wbc->wb_bytes += bytes;
 873                return;
 874        }
 875
 876        if (id == wbc->wb_lcand_id)
 877                wbc->wb_lcand_bytes += bytes;
 878
 879        /* Boyer-Moore majority vote algorithm */
 880        if (!wbc->wb_tcand_bytes)
 881                wbc->wb_tcand_id = id;
 882        if (id == wbc->wb_tcand_id)
 883                wbc->wb_tcand_bytes += bytes;
 884        else
 885                wbc->wb_tcand_bytes -= min(bytes, wbc->wb_tcand_bytes);
 886}
 887EXPORT_SYMBOL_GPL(wbc_account_cgroup_owner);
 888
 889/**
 890 * inode_congested - test whether an inode is congested
 891 * @inode: inode to test for congestion (may be NULL)
 892 * @cong_bits: mask of WB_[a]sync_congested bits to test
 893 *
 894 * Tests whether @inode is congested.  @cong_bits is the mask of congestion
 895 * bits to test and the return value is the mask of set bits.
 896 *
 897 * If cgroup writeback is enabled for @inode, the congestion state is
 898 * determined by whether the cgwb (cgroup bdi_writeback) for the blkcg
 899 * associated with @inode is congested; otherwise, the root wb's congestion
 900 * state is used.
 901 *
 902 * @inode is allowed to be NULL as this function is often called on
 903 * mapping->host which is NULL for the swapper space.
 904 */
 905int inode_congested(struct inode *inode, int cong_bits)
 906{
 907        /*
 908         * Once set, ->i_wb never becomes NULL while the inode is alive.
 909         * Start transaction iff ->i_wb is visible.
 910         */
 911        if (inode && inode_to_wb_is_valid(inode)) {
 912                struct bdi_writeback *wb;
 913                struct wb_lock_cookie lock_cookie = {};
 914                bool congested;
 915
 916                wb = unlocked_inode_to_wb_begin(inode, &lock_cookie);
 917                congested = wb_congested(wb, cong_bits);
 918                unlocked_inode_to_wb_end(inode, &lock_cookie);
 919                return congested;
 920        }
 921
 922        return wb_congested(&inode_to_bdi(inode)->wb, cong_bits);
 923}
 924EXPORT_SYMBOL_GPL(inode_congested);
 925
 926/**
 927 * wb_split_bdi_pages - split nr_pages to write according to bandwidth
 928 * @wb: target bdi_writeback to split @nr_pages to
 929 * @nr_pages: number of pages to write for the whole bdi
 930 *
 931 * Split @wb's portion of @nr_pages according to @wb's write bandwidth in
 932 * relation to the total write bandwidth of all wb's w/ dirty inodes on
 933 * @wb->bdi.
 934 */
 935static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
 936{
 937        unsigned long this_bw = wb->avg_write_bandwidth;
 938        unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth);
 939
 940        if (nr_pages == LONG_MAX)
 941                return LONG_MAX;
 942
 943        /*
 944         * This may be called on clean wb's and proportional distribution
 945         * may not make sense, just use the original @nr_pages in those
 946         * cases.  In general, we wanna err on the side of writing more.
 947         */
 948        if (!tot_bw || this_bw >= tot_bw)
 949                return nr_pages;
 950        else
 951                return DIV_ROUND_UP_ULL((u64)nr_pages * this_bw, tot_bw);
 952}
 953
 954/**
 955 * bdi_split_work_to_wbs - split a wb_writeback_work to all wb's of a bdi
 956 * @bdi: target backing_dev_info
 957 * @base_work: wb_writeback_work to issue
 958 * @skip_if_busy: skip wb's which already have writeback in progress
 959 *
 960 * Split and issue @base_work to all wb's (bdi_writeback's) of @bdi which
 961 * have dirty inodes.  If @base_work->nr_page isn't %LONG_MAX, it's
 962 * distributed to the busy wbs according to each wb's proportion in the
 963 * total active write bandwidth of @bdi.
 964 */
 965static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
 966                                  struct wb_writeback_work *base_work,
 967                                  bool skip_if_busy)
 968{
 969        struct bdi_writeback *last_wb = NULL;
 970        struct bdi_writeback *wb = list_entry(&bdi->wb_list,
 971                                              struct bdi_writeback, bdi_node);
 972
 973        might_sleep();
 974restart:
 975        rcu_read_lock();
 976        list_for_each_entry_continue_rcu(wb, &bdi->wb_list, bdi_node) {
 977                DEFINE_WB_COMPLETION(fallback_work_done, bdi);
 978                struct wb_writeback_work fallback_work;
 979                struct wb_writeback_work *work;
 980                long nr_pages;
 981
 982                if (last_wb) {
 983                        wb_put(last_wb);
 984                        last_wb = NULL;
 985                }
 986
 987                /* SYNC_ALL writes out I_DIRTY_TIME too */
 988                if (!wb_has_dirty_io(wb) &&
 989                    (base_work->sync_mode == WB_SYNC_NONE ||
 990                     list_empty(&wb->b_dirty_time)))
 991                        continue;
 992                if (skip_if_busy && writeback_in_progress(wb))
 993                        continue;
 994
 995                nr_pages = wb_split_bdi_pages(wb, base_work->nr_pages);
 996
 997                work = kmalloc(sizeof(*work), GFP_ATOMIC);
 998                if (work) {
 999                        *work = *base_work;
1000                        work->nr_pages = nr_pages;
1001                        work->auto_free = 1;
1002                        wb_queue_work(wb, work);
1003                        continue;
1004                }
1005
1006                /* alloc failed, execute synchronously using on-stack fallback */
1007                work = &fallback_work;
1008                *work = *base_work;
1009                work->nr_pages = nr_pages;
1010                work->auto_free = 0;
1011                work->done = &fallback_work_done;
1012
1013                wb_queue_work(wb, work);
1014
1015                /*
1016                 * Pin @wb so that it stays on @bdi->wb_list.  This allows
1017                 * continuing iteration from @wb after dropping and
1018                 * regrabbing rcu read lock.
1019                 */
1020                wb_get(wb);
1021                last_wb = wb;
1022
1023                rcu_read_unlock();
1024                wb_wait_for_completion(&fallback_work_done);
1025                goto restart;
1026        }
1027        rcu_read_unlock();
1028
1029        if (last_wb)
1030                wb_put(last_wb);
1031}
1032
1033/**
1034 * cgroup_writeback_by_id - initiate cgroup writeback from bdi and memcg IDs
1035 * @bdi_id: target bdi id
1036 * @memcg_id: target memcg css id
1037 * @nr: number of pages to write, 0 for best-effort dirty flushing
1038 * @reason: reason why some writeback work initiated
1039 * @done: target wb_completion
1040 *
1041 * Initiate flush of the bdi_writeback identified by @bdi_id and @memcg_id
1042 * with the specified parameters.
1043 */
1044int cgroup_writeback_by_id(u64 bdi_id, int memcg_id, unsigned long nr,
1045                           enum wb_reason reason, struct wb_completion *done)
1046{
1047        struct backing_dev_info *bdi;
1048        struct cgroup_subsys_state *memcg_css;
1049        struct bdi_writeback *wb;
1050        struct wb_writeback_work *work;
1051        int ret;
1052
1053        /* lookup bdi and memcg */
1054        bdi = bdi_get_by_id(bdi_id);
1055        if (!bdi)
1056                return -ENOENT;
1057
1058        rcu_read_lock();
1059        memcg_css = css_from_id(memcg_id, &memory_cgrp_subsys);
1060        if (memcg_css && !css_tryget(memcg_css))
1061                memcg_css = NULL;
1062        rcu_read_unlock();
1063        if (!memcg_css) {
1064                ret = -ENOENT;
1065                goto out_bdi_put;
1066        }
1067
1068        /*
1069         * And find the associated wb.  If the wb isn't there already
1070         * there's nothing to flush, don't create one.
1071         */
1072        wb = wb_get_lookup(bdi, memcg_css);
1073        if (!wb) {
1074                ret = -ENOENT;
1075                goto out_css_put;
1076        }
1077
1078        /*
1079         * If @nr is zero, the caller is attempting to write out most of
1080         * the currently dirty pages.  Let's take the current dirty page
1081         * count and inflate it by 25% which should be large enough to
1082         * flush out most dirty pages while avoiding getting livelocked by
1083         * concurrent dirtiers.
1084         */
1085        if (!nr) {
1086                unsigned long filepages, headroom, dirty, writeback;
1087
1088                mem_cgroup_wb_stats(wb, &filepages, &headroom, &dirty,
1089                                      &writeback);
1090                nr = dirty * 10 / 8;
1091        }
1092
1093        /* issue the writeback work */
1094        work = kzalloc(sizeof(*work), GFP_NOWAIT | __GFP_NOWARN);
1095        if (work) {
1096                work->nr_pages = nr;
1097                work->sync_mode = WB_SYNC_NONE;
1098                work->range_cyclic = 1;
1099                work->reason = reason;
1100                work->done = done;
1101                work->auto_free = 1;
1102                wb_queue_work(wb, work);
1103                ret = 0;
1104        } else {
1105                ret = -ENOMEM;
1106        }
1107
1108        wb_put(wb);
1109out_css_put:
1110        css_put(memcg_css);
1111out_bdi_put:
1112        bdi_put(bdi);
1113        return ret;
1114}
1115
1116/**
1117 * cgroup_writeback_umount - flush inode wb switches for umount
1118 *
1119 * This function is called when a super_block is about to be destroyed and
1120 * flushes in-flight inode wb switches.  An inode wb switch goes through
1121 * RCU and then workqueue, so the two need to be flushed in order to ensure
1122 * that all previously scheduled switches are finished.  As wb switches are
1123 * rare occurrences and synchronize_rcu() can take a while, perform
1124 * flushing iff wb switches are in flight.
1125 */
1126void cgroup_writeback_umount(void)
1127{
1128        /*
1129         * SB_ACTIVE should be reliably cleared before checking
1130         * isw_nr_in_flight, see generic_shutdown_super().
1131         */
1132        smp_mb();
1133
1134        if (atomic_read(&isw_nr_in_flight)) {
1135                /*
1136                 * Use rcu_barrier() to wait for all pending callbacks to
1137                 * ensure that all in-flight wb switches are in the workqueue.
1138                 */
1139                rcu_barrier();
1140                flush_workqueue(isw_wq);
1141        }
1142}
1143
1144static int __init cgroup_writeback_init(void)
1145{
1146        isw_wq = alloc_workqueue("inode_switch_wbs", 0, 0);
1147        if (!isw_wq)
1148                return -ENOMEM;
1149        return 0;
1150}
1151fs_initcall(cgroup_writeback_init);
1152
1153#else   /* CONFIG_CGROUP_WRITEBACK */
1154
1155static void bdi_down_write_wb_switch_rwsem(struct backing_dev_info *bdi) { }
1156static void bdi_up_write_wb_switch_rwsem(struct backing_dev_info *bdi) { }
1157
1158static void inode_cgwb_move_to_attached(struct inode *inode,
1159                                        struct bdi_writeback *wb)
1160{
1161        assert_spin_locked(&wb->list_lock);
1162        assert_spin_locked(&inode->i_lock);
1163
1164        inode->i_state &= ~I_SYNC_QUEUED;
1165        list_del_init(&inode->i_io_list);
1166        wb_io_lists_depopulated(wb);
1167}
1168
1169static struct bdi_writeback *
1170locked_inode_to_wb_and_lock_list(struct inode *inode)
1171        __releases(&inode->i_lock)
1172        __acquires(&wb->list_lock)
1173{
1174        struct bdi_writeback *wb = inode_to_wb(inode);
1175
1176        spin_unlock(&inode->i_lock);
1177        spin_lock(&wb->list_lock);
1178        return wb;
1179}
1180
1181static struct bdi_writeback *inode_to_wb_and_lock_list(struct inode *inode)
1182        __acquires(&wb->list_lock)
1183{
1184        struct bdi_writeback *wb = inode_to_wb(inode);
1185
1186        spin_lock(&wb->list_lock);
1187        return wb;
1188}
1189
1190static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
1191{
1192        return nr_pages;
1193}
1194
1195static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
1196                                  struct wb_writeback_work *base_work,
1197                                  bool skip_if_busy)
1198{
1199        might_sleep();
1200
1201        if (!skip_if_busy || !writeback_in_progress(&bdi->wb)) {
1202                base_work->auto_free = 0;
1203                wb_queue_work(&bdi->wb, base_work);
1204        }
1205}
1206
1207#endif  /* CONFIG_CGROUP_WRITEBACK */
1208
1209/*
1210 * Add in the number of potentially dirty inodes, because each inode
1211 * write can dirty pagecache in the underlying blockdev.
1212 */
1213static unsigned long get_nr_dirty_pages(void)
1214{
1215        return global_node_page_state(NR_FILE_DIRTY) +
1216                get_nr_dirty_inodes();
1217}
1218
1219static void wb_start_writeback(struct bdi_writeback *wb, enum wb_reason reason)
1220{
1221        if (!wb_has_dirty_io(wb))
1222                return;
1223
1224        /*
1225         * All callers of this function want to start writeback of all
1226         * dirty pages. Places like vmscan can call this at a very
1227         * high frequency, causing pointless allocations of tons of
1228         * work items and keeping the flusher threads busy retrieving
1229         * that work. Ensure that we only allow one of them pending and
1230         * inflight at the time.
1231         */
1232        if (test_bit(WB_start_all, &wb->state) ||
1233            test_and_set_bit(WB_start_all, &wb->state))
1234                return;
1235
1236        wb->start_all_reason = reason;
1237        wb_wakeup(wb);
1238}
1239
1240/**
1241 * wb_start_background_writeback - start background writeback
1242 * @wb: bdi_writback to write from
1243 *
1244 * Description:
1245 *   This makes sure WB_SYNC_NONE background writeback happens. When
1246 *   this function returns, it is only guaranteed that for given wb
1247 *   some IO is happening if we are over background dirty threshold.
1248 *   Caller need not hold sb s_umount semaphore.
1249 */
1250void wb_start_background_writeback(struct bdi_writeback *wb)
1251{
1252        /*
1253         * We just wake up the flusher thread. It will perform background
1254         * writeback as soon as there is no other work to do.
1255         */
1256        trace_writeback_wake_background(wb);
1257        wb_wakeup(wb);
1258}
1259
1260/*
1261 * Remove the inode from the writeback list it is on.
1262 */
1263void inode_io_list_del(struct inode *inode)
1264{
1265        struct bdi_writeback *wb;
1266
1267        wb = inode_to_wb_and_lock_list(inode);
1268        spin_lock(&inode->i_lock);
1269
1270        inode->i_state &= ~I_SYNC_QUEUED;
1271        list_del_init(&inode->i_io_list);
1272        wb_io_lists_depopulated(wb);
1273
1274        spin_unlock(&inode->i_lock);
1275        spin_unlock(&wb->list_lock);
1276}
1277EXPORT_SYMBOL(inode_io_list_del);
1278
1279/*
1280 * mark an inode as under writeback on the sb
1281 */
1282void sb_mark_inode_writeback(struct inode *inode)
1283{
1284        struct super_block *sb = inode->i_sb;
1285        unsigned long flags;
1286
1287        if (list_empty(&inode->i_wb_list)) {
1288                spin_lock_irqsave(&sb->s_inode_wblist_lock, flags);
1289                if (list_empty(&inode->i_wb_list)) {
1290                        list_add_tail(&inode->i_wb_list, &sb->s_inodes_wb);
1291                        trace_sb_mark_inode_writeback(inode);
1292                }
1293                spin_unlock_irqrestore(&sb->s_inode_wblist_lock, flags);
1294        }
1295}
1296
1297/*
1298 * clear an inode as under writeback on the sb
1299 */
1300void sb_clear_inode_writeback(struct inode *inode)
1301{
1302        struct super_block *sb = inode->i_sb;
1303        unsigned long flags;
1304
1305        if (!list_empty(&inode->i_wb_list)) {
1306                spin_lock_irqsave(&sb->s_inode_wblist_lock, flags);
1307                if (!list_empty(&inode->i_wb_list)) {
1308                        list_del_init(&inode->i_wb_list);
1309                        trace_sb_clear_inode_writeback(inode);
1310                }
1311                spin_unlock_irqrestore(&sb->s_inode_wblist_lock, flags);
1312        }
1313}
1314
1315/*
1316 * Redirty an inode: set its when-it-was dirtied timestamp and move it to the
1317 * furthest end of its superblock's dirty-inode list.
1318 *
1319 * Before stamping the inode's ->dirtied_when, we check to see whether it is
1320 * already the most-recently-dirtied inode on the b_dirty list.  If that is
1321 * the case then the inode must have been redirtied while it was being written
1322 * out and we don't reset its dirtied_when.
1323 */
1324static void redirty_tail_locked(struct inode *inode, struct bdi_writeback *wb)
1325{
1326        assert_spin_locked(&inode->i_lock);
1327
1328        if (!list_empty(&wb->b_dirty)) {
1329                struct inode *tail;
1330
1331                tail = wb_inode(wb->b_dirty.next);
1332                if (time_before(inode->dirtied_when, tail->dirtied_when))
1333                        inode->dirtied_when = jiffies;
1334        }
1335        inode_io_list_move_locked(inode, wb, &wb->b_dirty);
1336        inode->i_state &= ~I_SYNC_QUEUED;
1337}
1338
1339static void redirty_tail(struct inode *inode, struct bdi_writeback *wb)
1340{
1341        spin_lock(&inode->i_lock);
1342        redirty_tail_locked(inode, wb);
1343        spin_unlock(&inode->i_lock);
1344}
1345
1346/*
1347 * requeue inode for re-scanning after bdi->b_io list is exhausted.
1348 */
1349static void requeue_io(struct inode *inode, struct bdi_writeback *wb)
1350{
1351        inode_io_list_move_locked(inode, wb, &wb->b_more_io);
1352}
1353
1354static void inode_sync_complete(struct inode *inode)
1355{
1356        inode->i_state &= ~I_SYNC;
1357        /* If inode is clean an unused, put it into LRU now... */
1358        inode_add_lru(inode);
1359        /* Waiters must see I_SYNC cleared before being woken up */
1360        smp_mb();
1361        wake_up_bit(&inode->i_state, __I_SYNC);
1362}
1363
1364static bool inode_dirtied_after(struct inode *inode, unsigned long t)
1365{
1366        bool ret = time_after(inode->dirtied_when, t);
1367#ifndef CONFIG_64BIT
1368        /*
1369         * For inodes being constantly redirtied, dirtied_when can get stuck.
1370         * It _appears_ to be in the future, but is actually in distant past.
1371         * This test is necessary to prevent such wrapped-around relative times
1372         * from permanently stopping the whole bdi writeback.
1373         */
1374        ret = ret && time_before_eq(inode->dirtied_when, jiffies);
1375#endif
1376        return ret;
1377}
1378
1379#define EXPIRE_DIRTY_ATIME 0x0001
1380
1381/*
1382 * Move expired (dirtied before dirtied_before) dirty inodes from
1383 * @delaying_queue to @dispatch_queue.
1384 */
1385static int move_expired_inodes(struct list_head *delaying_queue,
1386                               struct list_head *dispatch_queue,
1387                               unsigned long dirtied_before)
1388{
1389        LIST_HEAD(tmp);
1390        struct list_head *pos, *node;
1391        struct super_block *sb = NULL;
1392        struct inode *inode;
1393        int do_sb_sort = 0;
1394        int moved = 0;
1395
1396        while (!list_empty(delaying_queue)) {
1397                inode = wb_inode(delaying_queue->prev);
1398                if (inode_dirtied_after(inode, dirtied_before))
1399                        break;
1400                list_move(&inode->i_io_list, &tmp);
1401                moved++;
1402                spin_lock(&inode->i_lock);
1403                inode->i_state |= I_SYNC_QUEUED;
1404                spin_unlock(&inode->i_lock);
1405                if (sb_is_blkdev_sb(inode->i_sb))
1406                        continue;
1407                if (sb && sb != inode->i_sb)
1408                        do_sb_sort = 1;
1409                sb = inode->i_sb;
1410        }
1411
1412        /* just one sb in list, splice to dispatch_queue and we're done */
1413        if (!do_sb_sort) {
1414                list_splice(&tmp, dispatch_queue);
1415                goto out;
1416        }
1417
1418        /* Move inodes from one superblock together */
1419        while (!list_empty(&tmp)) {
1420                sb = wb_inode(tmp.prev)->i_sb;
1421                list_for_each_prev_safe(pos, node, &tmp) {
1422                        inode = wb_inode(pos);
1423                        if (inode->i_sb == sb)
1424                                list_move(&inode->i_io_list, dispatch_queue);
1425                }
1426        }
1427out:
1428        return moved;
1429}
1430
1431/*
1432 * Queue all expired dirty inodes for io, eldest first.
1433 * Before
1434 *         newly dirtied     b_dirty    b_io    b_more_io
1435 *         =============>    gf         edc     BA
1436 * After
1437 *         newly dirtied     b_dirty    b_io    b_more_io
1438 *         =============>    g          fBAedc
1439 *                                           |
1440 *                                           +--> dequeue for IO
1441 */
1442static void queue_io(struct bdi_writeback *wb, struct wb_writeback_work *work,
1443                     unsigned long dirtied_before)
1444{
1445        int moved;
1446        unsigned long time_expire_jif = dirtied_before;
1447
1448        assert_spin_locked(&wb->list_lock);
1449        list_splice_init(&wb->b_more_io, &wb->b_io);
1450        moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, dirtied_before);
1451        if (!work->for_sync)
1452                time_expire_jif = jiffies - dirtytime_expire_interval * HZ;
1453        moved += move_expired_inodes(&wb->b_dirty_time, &wb->b_io,
1454                                     time_expire_jif);
1455        if (moved)
1456                wb_io_lists_populated(wb);
1457        trace_writeback_queue_io(wb, work, dirtied_before, moved);
1458}
1459
1460static int write_inode(struct inode *inode, struct writeback_control *wbc)
1461{
1462        int ret;
1463
1464        if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode)) {
1465                trace_writeback_write_inode_start(inode, wbc);
1466                ret = inode->i_sb->s_op->write_inode(inode, wbc);
1467                trace_writeback_write_inode(inode, wbc);
1468                return ret;
1469        }
1470        return 0;
1471}
1472
1473/*
1474 * Wait for writeback on an inode to complete. Called with i_lock held.
1475 * Caller must make sure inode cannot go away when we drop i_lock.
1476 */
1477static void __inode_wait_for_writeback(struct inode *inode)
1478        __releases(inode->i_lock)
1479        __acquires(inode->i_lock)
1480{
1481        DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
1482        wait_queue_head_t *wqh;
1483
1484        wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
1485        while (inode->i_state & I_SYNC) {
1486                spin_unlock(&inode->i_lock);
1487                __wait_on_bit(wqh, &wq, bit_wait,
1488                              TASK_UNINTERRUPTIBLE);
1489                spin_lock(&inode->i_lock);
1490        }
1491}
1492
1493/*
1494 * Wait for writeback on an inode to complete. Caller must have inode pinned.
1495 */
1496void inode_wait_for_writeback(struct inode *inode)
1497{
1498        spin_lock(&inode->i_lock);
1499        __inode_wait_for_writeback(inode);
1500        spin_unlock(&inode->i_lock);
1501}
1502
1503/*
1504 * Sleep until I_SYNC is cleared. This function must be called with i_lock
1505 * held and drops it. It is aimed for callers not holding any inode reference
1506 * so once i_lock is dropped, inode can go away.
1507 */
1508static void inode_sleep_on_writeback(struct inode *inode)
1509        __releases(inode->i_lock)
1510{
1511        DEFINE_WAIT(wait);
1512        wait_queue_head_t *wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
1513        int sleep;
1514
1515        prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
1516        sleep = inode->i_state & I_SYNC;
1517        spin_unlock(&inode->i_lock);
1518        if (sleep)
1519                schedule();
1520        finish_wait(wqh, &wait);
1521}
1522
1523/*
1524 * Find proper writeback list for the inode depending on its current state and
1525 * possibly also change of its state while we were doing writeback.  Here we
1526 * handle things such as livelock prevention or fairness of writeback among
1527 * inodes. This function can be called only by flusher thread - noone else
1528 * processes all inodes in writeback lists and requeueing inodes behind flusher
1529 * thread's back can have unexpected consequences.
1530 */
1531static void requeue_inode(struct inode *inode, struct bdi_writeback *wb,
1532                          struct writeback_control *wbc)
1533{
1534        if (inode->i_state & I_FREEING)
1535                return;
1536
1537        /*
1538         * Sync livelock prevention. Each inode is tagged and synced in one
1539         * shot. If still dirty, it will be redirty_tail()'ed below.  Update
1540         * the dirty time to prevent enqueue and sync it again.
1541         */
1542        if ((inode->i_state & I_DIRTY) &&
1543            (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages))
1544                inode->dirtied_when = jiffies;
1545
1546        if (wbc->pages_skipped) {
1547                /*
1548                 * writeback is not making progress due to locked
1549                 * buffers. Skip this inode for now.
1550                 */
1551                redirty_tail_locked(inode, wb);
1552                return;
1553        }
1554
1555        if (mapping_tagged(inode->i_mapping, PAGECACHE_TAG_DIRTY)) {
1556                /*
1557                 * We didn't write back all the pages.  nfs_writepages()
1558                 * sometimes bales out without doing anything.
1559                 */
1560                if (wbc->nr_to_write <= 0) {
1561                        /* Slice used up. Queue for next turn. */
1562                        requeue_io(inode, wb);
1563                } else {
1564                        /*
1565                         * Writeback blocked by something other than
1566                         * congestion. Delay the inode for some time to
1567                         * avoid spinning on the CPU (100% iowait)
1568                         * retrying writeback of the dirty page/inode
1569                         * that cannot be performed immediately.
1570                         */
1571                        redirty_tail_locked(inode, wb);
1572                }
1573        } else if (inode->i_state & I_DIRTY) {
1574                /*
1575                 * Filesystems can dirty the inode during writeback operations,
1576                 * such as delayed allocation during submission or metadata
1577                 * updates after data IO completion.
1578                 */
1579                redirty_tail_locked(inode, wb);
1580        } else if (inode->i_state & I_DIRTY_TIME) {
1581                inode->dirtied_when = jiffies;
1582                inode_io_list_move_locked(inode, wb, &wb->b_dirty_time);
1583                inode->i_state &= ~I_SYNC_QUEUED;
1584        } else {
1585                /* The inode is clean. Remove from writeback lists. */
1586                inode_cgwb_move_to_attached(inode, wb);
1587        }
1588}
1589
1590/*
1591 * Write out an inode and its dirty pages (or some of its dirty pages, depending
1592 * on @wbc->nr_to_write), and clear the relevant dirty flags from i_state.
1593 *
1594 * This doesn't remove the inode from the writeback list it is on, except
1595 * potentially to move it from b_dirty_time to b_dirty due to timestamp
1596 * expiration.  The caller is otherwise responsible for writeback list handling.
1597 *
1598 * The caller is also responsible for setting the I_SYNC flag beforehand and
1599 * calling inode_sync_complete() to clear it afterwards.
1600 */
1601static int
1602__writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
1603{
1604        struct address_space *mapping = inode->i_mapping;
1605        long nr_to_write = wbc->nr_to_write;
1606        unsigned dirty;
1607        int ret;
1608
1609        WARN_ON(!(inode->i_state & I_SYNC));
1610
1611        trace_writeback_single_inode_start(inode, wbc, nr_to_write);
1612
1613        ret = do_writepages(mapping, wbc);
1614
1615        /*
1616         * Make sure to wait on the data before writing out the metadata.
1617         * This is important for filesystems that modify metadata on data
1618         * I/O completion. We don't do it for sync(2) writeback because it has a
1619         * separate, external IO completion path and ->sync_fs for guaranteeing
1620         * inode metadata is written back correctly.
1621         */
1622        if (wbc->sync_mode == WB_SYNC_ALL && !wbc->for_sync) {
1623                int err = filemap_fdatawait(mapping);
1624                if (ret == 0)
1625                        ret = err;
1626        }
1627
1628        /*
1629         * If the inode has dirty timestamps and we need to write them, call
1630         * mark_inode_dirty_sync() to notify the filesystem about it and to
1631         * change I_DIRTY_TIME into I_DIRTY_SYNC.
1632         */
1633        if ((inode->i_state & I_DIRTY_TIME) &&
1634            (wbc->sync_mode == WB_SYNC_ALL ||
1635             time_after(jiffies, inode->dirtied_time_when +
1636                        dirtytime_expire_interval * HZ))) {
1637                trace_writeback_lazytime(inode);
1638                mark_inode_dirty_sync(inode);
1639        }
1640
1641        /*
1642         * Get and clear the dirty flags from i_state.  This needs to be done
1643         * after calling writepages because some filesystems may redirty the
1644         * inode during writepages due to delalloc.  It also needs to be done
1645         * after handling timestamp expiration, as that may dirty the inode too.
1646         */
1647        spin_lock(&inode->i_lock);
1648        dirty = inode->i_state & I_DIRTY;
1649        inode->i_state &= ~dirty;
1650
1651        /*
1652         * Paired with smp_mb() in __mark_inode_dirty().  This allows
1653         * __mark_inode_dirty() to test i_state without grabbing i_lock -
1654         * either they see the I_DIRTY bits cleared or we see the dirtied
1655         * inode.
1656         *
1657         * I_DIRTY_PAGES is always cleared together above even if @mapping
1658         * still has dirty pages.  The flag is reinstated after smp_mb() if
1659         * necessary.  This guarantees that either __mark_inode_dirty()
1660         * sees clear I_DIRTY_PAGES or we see PAGECACHE_TAG_DIRTY.
1661         */
1662        smp_mb();
1663
1664        if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
1665                inode->i_state |= I_DIRTY_PAGES;
1666
1667        spin_unlock(&inode->i_lock);
1668
1669        /* Don't write the inode if only I_DIRTY_PAGES was set */
1670        if (dirty & ~I_DIRTY_PAGES) {
1671                int err = write_inode(inode, wbc);
1672                if (ret == 0)
1673                        ret = err;
1674        }
1675        trace_writeback_single_inode(inode, wbc, nr_to_write);
1676        return ret;
1677}
1678
1679/*
1680 * Write out an inode's dirty data and metadata on-demand, i.e. separately from
1681 * the regular batched writeback done by the flusher threads in
1682 * writeback_sb_inodes().  @wbc controls various aspects of the write, such as
1683 * whether it is a data-integrity sync (%WB_SYNC_ALL) or not (%WB_SYNC_NONE).
1684 *
1685 * To prevent the inode from going away, either the caller must have a reference
1686 * to the inode, or the inode must have I_WILL_FREE or I_FREEING set.
1687 */
1688static int writeback_single_inode(struct inode *inode,
1689                                  struct writeback_control *wbc)
1690{
1691        struct bdi_writeback *wb;
1692        int ret = 0;
1693
1694        spin_lock(&inode->i_lock);
1695        if (!atomic_read(&inode->i_count))
1696                WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
1697        else
1698                WARN_ON(inode->i_state & I_WILL_FREE);
1699
1700        if (inode->i_state & I_SYNC) {
1701                /*
1702                 * Writeback is already running on the inode.  For WB_SYNC_NONE,
1703                 * that's enough and we can just return.  For WB_SYNC_ALL, we
1704                 * must wait for the existing writeback to complete, then do
1705                 * writeback again if there's anything left.
1706                 */
1707                if (wbc->sync_mode != WB_SYNC_ALL)
1708                        goto out;
1709                __inode_wait_for_writeback(inode);
1710        }
1711        WARN_ON(inode->i_state & I_SYNC);
1712        /*
1713         * If the inode is already fully clean, then there's nothing to do.
1714         *
1715         * For data-integrity syncs we also need to check whether any pages are
1716         * still under writeback, e.g. due to prior WB_SYNC_NONE writeback.  If
1717         * there are any such pages, we'll need to wait for them.
1718         */
1719        if (!(inode->i_state & I_DIRTY_ALL) &&
1720            (wbc->sync_mode != WB_SYNC_ALL ||
1721             !mapping_tagged(inode->i_mapping, PAGECACHE_TAG_WRITEBACK)))
1722                goto out;
1723        inode->i_state |= I_SYNC;
1724        wbc_attach_and_unlock_inode(wbc, inode);
1725
1726        ret = __writeback_single_inode(inode, wbc);
1727
1728        wbc_detach_inode(wbc);
1729
1730        wb = inode_to_wb_and_lock_list(inode);
1731        spin_lock(&inode->i_lock);
1732        /*
1733         * If the inode is now fully clean, then it can be safely removed from
1734         * its writeback list (if any).  Otherwise the flusher threads are
1735         * responsible for the writeback lists.
1736         */
1737        if (!(inode->i_state & I_DIRTY_ALL))
1738                inode_cgwb_move_to_attached(inode, wb);
1739        spin_unlock(&wb->list_lock);
1740        inode_sync_complete(inode);
1741out:
1742        spin_unlock(&inode->i_lock);
1743        return ret;
1744}
1745
1746static long writeback_chunk_size(struct bdi_writeback *wb,
1747                                 struct wb_writeback_work *work)
1748{
1749        long pages;
1750
1751        /*
1752         * WB_SYNC_ALL mode does livelock avoidance by syncing dirty
1753         * inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
1754         * here avoids calling into writeback_inodes_wb() more than once.
1755         *
1756         * The intended call sequence for WB_SYNC_ALL writeback is:
1757         *
1758         *      wb_writeback()
1759         *          writeback_sb_inodes()       <== called only once
1760         *              write_cache_pages()     <== called once for each inode
1761         *                   (quickly) tag currently dirty pages
1762         *                   (maybe slowly) sync all tagged pages
1763         */
1764        if (work->sync_mode == WB_SYNC_ALL || work->tagged_writepages)
1765                pages = LONG_MAX;
1766        else {
1767                pages = min(wb->avg_write_bandwidth / 2,
1768                            global_wb_domain.dirty_limit / DIRTY_SCOPE);
1769                pages = min(pages, work->nr_pages);
1770                pages = round_down(pages + MIN_WRITEBACK_PAGES,
1771                                   MIN_WRITEBACK_PAGES);
1772        }
1773
1774        return pages;
1775}
1776
1777/*
1778 * Write a portion of b_io inodes which belong to @sb.
1779 *
1780 * Return the number of pages and/or inodes written.
1781 *
1782 * NOTE! This is called with wb->list_lock held, and will
1783 * unlock and relock that for each inode it ends up doing
1784 * IO for.
1785 */
1786static long writeback_sb_inodes(struct super_block *sb,
1787                                struct bdi_writeback *wb,
1788                                struct wb_writeback_work *work)
1789{
1790        struct writeback_control wbc = {
1791                .sync_mode              = work->sync_mode,
1792                .tagged_writepages      = work->tagged_writepages,
1793                .for_kupdate            = work->for_kupdate,
1794                .for_background         = work->for_background,
1795                .for_sync               = work->for_sync,
1796                .range_cyclic           = work->range_cyclic,
1797                .range_start            = 0,
1798                .range_end              = LLONG_MAX,
1799        };
1800        unsigned long start_time = jiffies;
1801        long write_chunk;
1802        long wrote = 0;  /* count both pages and inodes */
1803
1804        while (!list_empty(&wb->b_io)) {
1805                struct inode *inode = wb_inode(wb->b_io.prev);
1806                struct bdi_writeback *tmp_wb;
1807
1808                if (inode->i_sb != sb) {
1809                        if (work->sb) {
1810                                /*
1811                                 * We only want to write back data for this
1812                                 * superblock, move all inodes not belonging
1813                                 * to it back onto the dirty list.
1814                                 */
1815                                redirty_tail(inode, wb);
1816                                continue;
1817                        }
1818
1819                        /*
1820                         * The inode belongs to a different superblock.
1821                         * Bounce back to the caller to unpin this and
1822                         * pin the next superblock.
1823                         */
1824                        break;
1825                }
1826
1827                /*
1828                 * Don't bother with new inodes or inodes being freed, first
1829                 * kind does not need periodic writeout yet, and for the latter
1830                 * kind writeout is handled by the freer.
1831                 */
1832                spin_lock(&inode->i_lock);
1833                if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
1834                        redirty_tail_locked(inode, wb);
1835                        spin_unlock(&inode->i_lock);
1836                        continue;
1837                }
1838                if ((inode->i_state & I_SYNC) && wbc.sync_mode != WB_SYNC_ALL) {
1839                        /*
1840                         * If this inode is locked for writeback and we are not
1841                         * doing writeback-for-data-integrity, move it to
1842                         * b_more_io so that writeback can proceed with the
1843                         * other inodes on s_io.
1844                         *
1845                         * We'll have another go at writing back this inode
1846                         * when we completed a full scan of b_io.
1847                         */
1848                        spin_unlock(&inode->i_lock);
1849                        requeue_io(inode, wb);
1850                        trace_writeback_sb_inodes_requeue(inode);
1851                        continue;
1852                }
1853                spin_unlock(&wb->list_lock);
1854
1855                /*
1856                 * We already requeued the inode if it had I_SYNC set and we
1857                 * are doing WB_SYNC_NONE writeback. So this catches only the
1858                 * WB_SYNC_ALL case.
1859                 */
1860                if (inode->i_state & I_SYNC) {
1861                        /* Wait for I_SYNC. This function drops i_lock... */
1862                        inode_sleep_on_writeback(inode);
1863                        /* Inode may be gone, start again */
1864                        spin_lock(&wb->list_lock);
1865                        continue;
1866                }
1867                inode->i_state |= I_SYNC;
1868                wbc_attach_and_unlock_inode(&wbc, inode);
1869
1870                write_chunk = writeback_chunk_size(wb, work);
1871                wbc.nr_to_write = write_chunk;
1872                wbc.pages_skipped = 0;
1873
1874                /*
1875                 * We use I_SYNC to pin the inode in memory. While it is set
1876                 * evict_inode() will wait so the inode cannot be freed.
1877                 */
1878                __writeback_single_inode(inode, &wbc);
1879
1880                wbc_detach_inode(&wbc);
1881                work->nr_pages -= write_chunk - wbc.nr_to_write;
1882                wrote += write_chunk - wbc.nr_to_write;
1883
1884                if (need_resched()) {
1885                        /*
1886                         * We're trying to balance between building up a nice
1887                         * long list of IOs to improve our merge rate, and
1888                         * getting those IOs out quickly for anyone throttling
1889                         * in balance_dirty_pages().  cond_resched() doesn't
1890                         * unplug, so get our IOs out the door before we
1891                         * give up the CPU.
1892                         */
1893                        blk_flush_plug(current);
1894                        cond_resched();
1895                }
1896
1897                /*
1898                 * Requeue @inode if still dirty.  Be careful as @inode may
1899                 * have been switched to another wb in the meantime.
1900                 */
1901                tmp_wb = inode_to_wb_and_lock_list(inode);
1902                spin_lock(&inode->i_lock);
1903                if (!(inode->i_state & I_DIRTY_ALL))
1904                        wrote++;
1905                requeue_inode(inode, tmp_wb, &wbc);
1906                inode_sync_complete(inode);
1907                spin_unlock(&inode->i_lock);
1908
1909                if (unlikely(tmp_wb != wb)) {
1910                        spin_unlock(&tmp_wb->list_lock);
1911                        spin_lock(&wb->list_lock);
1912                }
1913
1914                /*
1915                 * bail out to wb_writeback() often enough to check
1916                 * background threshold and other termination conditions.
1917                 */
1918                if (wrote) {
1919                        if (time_is_before_jiffies(start_time + HZ / 10UL))
1920                                break;
1921                        if (work->nr_pages <= 0)
1922                                break;
1923                }
1924        }
1925        return wrote;
1926}
1927
1928static long __writeback_inodes_wb(struct bdi_writeback *wb,
1929                                  struct wb_writeback_work *work)
1930{
1931        unsigned long start_time = jiffies;
1932        long wrote = 0;
1933
1934        while (!list_empty(&wb->b_io)) {
1935                struct inode *inode = wb_inode(wb->b_io.prev);
1936                struct super_block *sb = inode->i_sb;
1937
1938                if (!trylock_super(sb)) {
1939                        /*
1940                         * trylock_super() may fail consistently due to
1941                         * s_umount being grabbed by someone else. Don't use
1942                         * requeue_io() to avoid busy retrying the inode/sb.
1943                         */
1944                        redirty_tail(inode, wb);
1945                        continue;
1946                }
1947                wrote += writeback_sb_inodes(sb, wb, work);
1948                up_read(&sb->s_umount);
1949
1950                /* refer to the same tests at the end of writeback_sb_inodes */
1951                if (wrote) {
1952                        if (time_is_before_jiffies(start_time + HZ / 10UL))
1953                                break;
1954                        if (work->nr_pages <= 0)
1955                                break;
1956                }
1957        }
1958        /* Leave any unwritten inodes on b_io */
1959        return wrote;
1960}
1961
1962static long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
1963                                enum wb_reason reason)
1964{
1965        struct wb_writeback_work work = {
1966                .nr_pages       = nr_pages,
1967                .sync_mode      = WB_SYNC_NONE,
1968                .range_cyclic   = 1,
1969                .reason         = reason,
1970        };
1971        struct blk_plug plug;
1972
1973        blk_start_plug(&plug);
1974        spin_lock(&wb->list_lock);
1975        if (list_empty(&wb->b_io))
1976                queue_io(wb, &work, jiffies);
1977        __writeback_inodes_wb(wb, &work);
1978        spin_unlock(&wb->list_lock);
1979        blk_finish_plug(&plug);
1980
1981        return nr_pages - work.nr_pages;
1982}
1983
1984/*
1985 * Explicit flushing or periodic writeback of "old" data.
1986 *
1987 * Define "old": the first time one of an inode's pages is dirtied, we mark the
1988 * dirtying-time in the inode's address_space.  So this periodic writeback code
1989 * just walks the superblock inode list, writing back any inodes which are
1990 * older than a specific point in time.
1991 *
1992 * Try to run once per dirty_writeback_interval.  But if a writeback event
1993 * takes longer than a dirty_writeback_interval interval, then leave a
1994 * one-second gap.
1995 *
1996 * dirtied_before takes precedence over nr_to_write.  So we'll only write back
1997 * all dirty pages if they are all attached to "old" mappings.
1998 */
1999static long wb_writeback(struct bdi_writeback *wb,
2000                         struct wb_writeback_work *work)
2001{
2002        unsigned long wb_start = jiffies;
2003        long nr_pages = work->nr_pages;
2004        unsigned long dirtied_before = jiffies;
2005        struct inode *inode;
2006        long progress;
2007        struct blk_plug plug;
2008
2009        blk_start_plug(&plug);
2010        spin_lock(&wb->list_lock);
2011        for (;;) {
2012                /*
2013                 * Stop writeback when nr_pages has been consumed
2014                 */
2015                if (work->nr_pages <= 0)
2016                        break;
2017
2018                /*
2019                 * Background writeout and kupdate-style writeback may
2020                 * run forever. Stop them if there is other work to do
2021                 * so that e.g. sync can proceed. They'll be restarted
2022                 * after the other works are all done.
2023                 */
2024                if ((work->for_background || work->for_kupdate) &&
2025                    !list_empty(&wb->work_list))
2026                        break;
2027
2028                /*
2029                 * For background writeout, stop when we are below the
2030                 * background dirty threshold
2031                 */
2032                if (work->for_background && !wb_over_bg_thresh(wb))
2033                        break;
2034
2035                /*
2036                 * Kupdate and background works are special and we want to
2037                 * include all inodes that need writing. Livelock avoidance is
2038                 * handled by these works yielding to any other work so we are
2039                 * safe.
2040                 */
2041                if (work->for_kupdate) {
2042                        dirtied_before = jiffies -
2043                                msecs_to_jiffies(dirty_expire_interval * 10);
2044                } else if (work->for_background)
2045                        dirtied_before = jiffies;
2046
2047                trace_writeback_start(wb, work);
2048                if (list_empty(&wb->b_io))
2049                        queue_io(wb, work, dirtied_before);
2050                if (work->sb)
2051                        progress = writeback_sb_inodes(work->sb, wb, work);
2052                else
2053                        progress = __writeback_inodes_wb(wb, work);
2054                trace_writeback_written(wb, work);
2055
2056                wb_update_bandwidth(wb, wb_start);
2057
2058                /*
2059                 * Did we write something? Try for more
2060                 *
2061                 * Dirty inodes are moved to b_io for writeback in batches.
2062                 * The completion of the current batch does not necessarily
2063                 * mean the overall work is done. So we keep looping as long
2064                 * as made some progress on cleaning pages or inodes.
2065                 */
2066                if (progress)
2067                        continue;
2068                /*
2069                 * No more inodes for IO, bail
2070                 */
2071                if (list_empty(&wb->b_more_io))
2072                        break;
2073                /*
2074                 * Nothing written. Wait for some inode to
2075                 * become available for writeback. Otherwise
2076                 * we'll just busyloop.
2077                 */
2078                trace_writeback_wait(wb, work);
2079                inode = wb_inode(wb->b_more_io.prev);
2080                spin_lock(&inode->i_lock);
2081                spin_unlock(&wb->list_lock);
2082                /* This function drops i_lock... */
2083                inode_sleep_on_writeback(inode);
2084                spin_lock(&wb->list_lock);
2085        }
2086        spin_unlock(&wb->list_lock);
2087        blk_finish_plug(&plug);
2088
2089        return nr_pages - work->nr_pages;
2090}
2091
2092/*
2093 * Return the next wb_writeback_work struct that hasn't been processed yet.
2094 */
2095static struct wb_writeback_work *get_next_work_item(struct bdi_writeback *wb)
2096{
2097        struct wb_writeback_work *work = NULL;
2098
2099        spin_lock_bh(&wb->work_lock);
2100        if (!list_empty(&wb->work_list)) {
2101                work = list_entry(wb->work_list.next,
2102                                  struct wb_writeback_work, list);
2103                list_del_init(&work->list);
2104        }
2105        spin_unlock_bh(&wb->work_lock);
2106        return work;
2107}
2108
2109static long wb_check_background_flush(struct bdi_writeback *wb)
2110{
2111        if (wb_over_bg_thresh(wb)) {
2112
2113                struct wb_writeback_work work = {
2114                        .nr_pages       = LONG_MAX,
2115                        .sync_mode      = WB_SYNC_NONE,
2116                        .for_background = 1,
2117                        .range_cyclic   = 1,
2118                        .reason         = WB_REASON_BACKGROUND,
2119                };
2120
2121                return wb_writeback(wb, &work);
2122        }
2123
2124        return 0;
2125}
2126
2127static long wb_check_old_data_flush(struct bdi_writeback *wb)
2128{
2129        unsigned long expired;
2130        long nr_pages;
2131
2132        /*
2133         * When set to zero, disable periodic writeback
2134         */
2135        if (!dirty_writeback_interval)
2136                return 0;
2137
2138        expired = wb->last_old_flush +
2139                        msecs_to_jiffies(dirty_writeback_interval * 10);
2140        if (time_before(jiffies, expired))
2141                return 0;
2142
2143        wb->last_old_flush = jiffies;
2144        nr_pages = get_nr_dirty_pages();
2145
2146        if (nr_pages) {
2147                struct wb_writeback_work work = {
2148                        .nr_pages       = nr_pages,
2149                        .sync_mode      = WB_SYNC_NONE,
2150                        .for_kupdate    = 1,
2151                        .range_cyclic   = 1,
2152                        .reason         = WB_REASON_PERIODIC,
2153                };
2154
2155                return wb_writeback(wb, &work);
2156        }
2157
2158        return 0;
2159}
2160
2161static long wb_check_start_all(struct bdi_writeback *wb)
2162{
2163        long nr_pages;
2164
2165        if (!test_bit(WB_start_all, &wb->state))
2166                return 0;
2167
2168        nr_pages = get_nr_dirty_pages();
2169        if (nr_pages) {
2170                struct wb_writeback_work work = {
2171                        .nr_pages       = wb_split_bdi_pages(wb, nr_pages),
2172                        .sync_mode      = WB_SYNC_NONE,
2173                        .range_cyclic   = 1,
2174                        .reason         = wb->start_all_reason,
2175                };
2176
2177                nr_pages = wb_writeback(wb, &work);
2178        }
2179
2180        clear_bit(WB_start_all, &wb->state);
2181        return nr_pages;
2182}
2183
2184
2185/*
2186 * Retrieve work items and do the writeback they describe
2187 */
2188static long wb_do_writeback(struct bdi_writeback *wb)
2189{
2190        struct wb_writeback_work *work;
2191        long wrote = 0;
2192
2193        set_bit(WB_writeback_running, &wb->state);
2194        while ((work = get_next_work_item(wb)) != NULL) {
2195                trace_writeback_exec(wb, work);
2196                wrote += wb_writeback(wb, work);
2197                finish_writeback_work(wb, work);
2198        }
2199
2200        /*
2201         * Check for a flush-everything request
2202         */
2203        wrote += wb_check_start_all(wb);
2204
2205        /*
2206         * Check for periodic writeback, kupdated() style
2207         */
2208        wrote += wb_check_old_data_flush(wb);
2209        wrote += wb_check_background_flush(wb);
2210        clear_bit(WB_writeback_running, &wb->state);
2211
2212        return wrote;
2213}
2214
2215/*
2216 * Handle writeback of dirty data for the device backed by this bdi. Also
2217 * reschedules periodically and does kupdated style flushing.
2218 */
2219void wb_workfn(struct work_struct *work)
2220{
2221        struct bdi_writeback *wb = container_of(to_delayed_work(work),
2222                                                struct bdi_writeback, dwork);
2223        long pages_written;
2224
2225        set_worker_desc("flush-%s", bdi_dev_name(wb->bdi));
2226        current->flags |= PF_SWAPWRITE;
2227
2228        if (likely(!current_is_workqueue_rescuer() ||
2229                   !test_bit(WB_registered, &wb->state))) {
2230                /*
2231                 * The normal path.  Keep writing back @wb until its
2232                 * work_list is empty.  Note that this path is also taken
2233                 * if @wb is shutting down even when we're running off the
2234                 * rescuer as work_list needs to be drained.
2235                 */
2236                do {
2237                        pages_written = wb_do_writeback(wb);
2238                        trace_writeback_pages_written(pages_written);
2239                } while (!list_empty(&wb->work_list));
2240        } else {
2241                /*
2242                 * bdi_wq can't get enough workers and we're running off
2243                 * the emergency worker.  Don't hog it.  Hopefully, 1024 is
2244                 * enough for efficient IO.
2245                 */
2246                pages_written = writeback_inodes_wb(wb, 1024,
2247                                                    WB_REASON_FORKER_THREAD);
2248                trace_writeback_pages_written(pages_written);
2249        }
2250
2251        if (!list_empty(&wb->work_list))
2252                wb_wakeup(wb);
2253        else if (wb_has_dirty_io(wb) && dirty_writeback_interval)
2254                wb_wakeup_delayed(wb);
2255
2256        current->flags &= ~PF_SWAPWRITE;
2257}
2258
2259/*
2260 * Start writeback of `nr_pages' pages on this bdi. If `nr_pages' is zero,
2261 * write back the whole world.
2262 */
2263static void __wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
2264                                         enum wb_reason reason)
2265{
2266        struct bdi_writeback *wb;
2267
2268        if (!bdi_has_dirty_io(bdi))
2269                return;
2270
2271        list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node)
2272                wb_start_writeback(wb, reason);
2273}
2274
2275void wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
2276                                enum wb_reason reason)
2277{
2278        rcu_read_lock();
2279        __wakeup_flusher_threads_bdi(bdi, reason);
2280        rcu_read_unlock();
2281}
2282
2283/*
2284 * Wakeup the flusher threads to start writeback of all currently dirty pages
2285 */
2286void wakeup_flusher_threads(enum wb_reason reason)
2287{
2288        struct backing_dev_info *bdi;
2289
2290        /*
2291         * If we are expecting writeback progress we must submit plugged IO.
2292         */
2293        if (blk_needs_flush_plug(current))
2294                blk_schedule_flush_plug(current);
2295
2296        rcu_read_lock();
2297        list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
2298                __wakeup_flusher_threads_bdi(bdi, reason);
2299        rcu_read_unlock();
2300}
2301
2302/*
2303 * Wake up bdi's periodically to make sure dirtytime inodes gets
2304 * written back periodically.  We deliberately do *not* check the
2305 * b_dirtytime list in wb_has_dirty_io(), since this would cause the
2306 * kernel to be constantly waking up once there are any dirtytime
2307 * inodes on the system.  So instead we define a separate delayed work
2308 * function which gets called much more rarely.  (By default, only
2309 * once every 12 hours.)
2310 *
2311 * If there is any other write activity going on in the file system,
2312 * this function won't be necessary.  But if the only thing that has
2313 * happened on the file system is a dirtytime inode caused by an atime
2314 * update, we need this infrastructure below to make sure that inode
2315 * eventually gets pushed out to disk.
2316 */
2317static void wakeup_dirtytime_writeback(struct work_struct *w);
2318static DECLARE_DELAYED_WORK(dirtytime_work, wakeup_dirtytime_writeback);
2319
2320static void wakeup_dirtytime_writeback(struct work_struct *w)
2321{
2322        struct backing_dev_info *bdi;
2323
2324        rcu_read_lock();
2325        list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
2326                struct bdi_writeback *wb;
2327
2328                list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node)
2329                        if (!list_empty(&wb->b_dirty_time))
2330                                wb_wakeup(wb);
2331        }
2332        rcu_read_unlock();
2333        schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
2334}
2335
2336static int __init start_dirtytime_writeback(void)
2337{
2338        schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
2339        return 0;
2340}
2341__initcall(start_dirtytime_writeback);
2342
2343int dirtytime_interval_handler(struct ctl_table *table, int write,
2344                               void *buffer, size_t *lenp, loff_t *ppos)
2345{
2346        int ret;
2347
2348        ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
2349        if (ret == 0 && write)
2350                mod_delayed_work(system_wq, &dirtytime_work, 0);
2351        return ret;
2352}
2353
2354/**
2355 * __mark_inode_dirty - internal function to mark an inode dirty
2356 *
2357 * @inode: inode to mark
2358 * @flags: what kind of dirty, e.g. I_DIRTY_SYNC.  This can be a combination of
2359 *         multiple I_DIRTY_* flags, except that I_DIRTY_TIME can't be combined
2360 *         with I_DIRTY_PAGES.
2361 *
2362 * Mark an inode as dirty.  We notify the filesystem, then update the inode's
2363 * dirty flags.  Then, if needed we add the inode to the appropriate dirty list.
2364 *
2365 * Most callers should use mark_inode_dirty() or mark_inode_dirty_sync()
2366 * instead of calling this directly.
2367 *
2368 * CAREFUL!  We only add the inode to the dirty list if it is hashed or if it
2369 * refers to a blockdev.  Unhashed inodes will never be added to the dirty list
2370 * even if they are later hashed, as they will have been marked dirty already.
2371 *
2372 * In short, ensure you hash any inodes _before_ you start marking them dirty.
2373 *
2374 * Note that for blockdevs, inode->dirtied_when represents the dirtying time of
2375 * the block-special inode (/dev/hda1) itself.  And the ->dirtied_when field of
2376 * the kernel-internal blockdev inode represents the dirtying time of the
2377 * blockdev's pages.  This is why for I_DIRTY_PAGES we always use
2378 * page->mapping->host, so the page-dirtying time is recorded in the internal
2379 * blockdev inode.
2380 */
2381void __mark_inode_dirty(struct inode *inode, int flags)
2382{
2383        struct super_block *sb = inode->i_sb;
2384        int dirtytime = 0;
2385
2386        trace_writeback_mark_inode_dirty(inode, flags);
2387
2388        if (flags & I_DIRTY_INODE) {
2389                /*
2390                 * Notify the filesystem about the inode being dirtied, so that
2391                 * (if needed) it can update on-disk fields and journal the
2392                 * inode.  This is only needed when the inode itself is being
2393                 * dirtied now.  I.e. it's only needed for I_DIRTY_INODE, not
2394                 * for just I_DIRTY_PAGES or I_DIRTY_TIME.
2395                 */
2396                trace_writeback_dirty_inode_start(inode, flags);
2397                if (sb->s_op->dirty_inode)
2398                        sb->s_op->dirty_inode(inode, flags & I_DIRTY_INODE);
2399                trace_writeback_dirty_inode(inode, flags);
2400
2401                /* I_DIRTY_INODE supersedes I_DIRTY_TIME. */
2402                flags &= ~I_DIRTY_TIME;
2403        } else {
2404                /*
2405                 * Else it's either I_DIRTY_PAGES, I_DIRTY_TIME, or nothing.
2406                 * (We don't support setting both I_DIRTY_PAGES and I_DIRTY_TIME
2407                 * in one call to __mark_inode_dirty().)
2408                 */
2409                dirtytime = flags & I_DIRTY_TIME;
2410                WARN_ON_ONCE(dirtytime && flags != I_DIRTY_TIME);
2411        }
2412
2413        /*
2414         * Paired with smp_mb() in __writeback_single_inode() for the
2415         * following lockless i_state test.  See there for details.
2416         */
2417        smp_mb();
2418
2419        if (((inode->i_state & flags) == flags) ||
2420            (dirtytime && (inode->i_state & I_DIRTY_INODE)))
2421                return;
2422
2423        spin_lock(&inode->i_lock);
2424        if (dirtytime && (inode->i_state & I_DIRTY_INODE))
2425                goto out_unlock_inode;
2426        if ((inode->i_state & flags) != flags) {
2427                const int was_dirty = inode->i_state & I_DIRTY;
2428
2429                inode_attach_wb(inode, NULL);
2430
2431                /* I_DIRTY_INODE supersedes I_DIRTY_TIME. */
2432                if (flags & I_DIRTY_INODE)
2433                        inode->i_state &= ~I_DIRTY_TIME;
2434                inode->i_state |= flags;
2435
2436                /*
2437                 * If the inode is queued for writeback by flush worker, just
2438                 * update its dirty state. Once the flush worker is done with
2439                 * the inode it will place it on the appropriate superblock
2440                 * list, based upon its state.
2441                 */
2442                if (inode->i_state & I_SYNC_QUEUED)
2443                        goto out_unlock_inode;
2444
2445                /*
2446                 * Only add valid (hashed) inodes to the superblock's
2447                 * dirty list.  Add blockdev inodes as well.
2448                 */
2449                if (!S_ISBLK(inode->i_mode)) {
2450                        if (inode_unhashed(inode))
2451                                goto out_unlock_inode;
2452                }
2453                if (inode->i_state & I_FREEING)
2454                        goto out_unlock_inode;
2455
2456                /*
2457                 * If the inode was already on b_dirty/b_io/b_more_io, don't
2458                 * reposition it (that would break b_dirty time-ordering).
2459                 */
2460                if (!was_dirty) {
2461                        struct bdi_writeback *wb;
2462                        struct list_head *dirty_list;
2463                        bool wakeup_bdi = false;
2464
2465                        wb = locked_inode_to_wb_and_lock_list(inode);
2466
2467                        inode->dirtied_when = jiffies;
2468                        if (dirtytime)
2469                                inode->dirtied_time_when = jiffies;
2470
2471                        if (inode->i_state & I_DIRTY)
2472                                dirty_list = &wb->b_dirty;
2473                        else
2474                                dirty_list = &wb->b_dirty_time;
2475
2476                        wakeup_bdi = inode_io_list_move_locked(inode, wb,
2477                                                               dirty_list);
2478
2479                        spin_unlock(&wb->list_lock);
2480                        trace_writeback_dirty_inode_enqueue(inode);
2481
2482                        /*
2483                         * If this is the first dirty inode for this bdi,
2484                         * we have to wake-up the corresponding bdi thread
2485                         * to make sure background write-back happens
2486                         * later.
2487                         */
2488                        if (wakeup_bdi &&
2489                            (wb->bdi->capabilities & BDI_CAP_WRITEBACK))
2490                                wb_wakeup_delayed(wb);
2491                        return;
2492                }
2493        }
2494out_unlock_inode:
2495        spin_unlock(&inode->i_lock);
2496}
2497EXPORT_SYMBOL(__mark_inode_dirty);
2498
2499/*
2500 * The @s_sync_lock is used to serialise concurrent sync operations
2501 * to avoid lock contention problems with concurrent wait_sb_inodes() calls.
2502 * Concurrent callers will block on the s_sync_lock rather than doing contending
2503 * walks. The queueing maintains sync(2) required behaviour as all the IO that
2504 * has been issued up to the time this function is enter is guaranteed to be
2505 * completed by the time we have gained the lock and waited for all IO that is
2506 * in progress regardless of the order callers are granted the lock.
2507 */
2508static void wait_sb_inodes(struct super_block *sb)
2509{
2510        LIST_HEAD(sync_list);
2511
2512        /*
2513         * We need to be protected against the filesystem going from
2514         * r/o to r/w or vice versa.
2515         */
2516        WARN_ON(!rwsem_is_locked(&sb->s_umount));
2517
2518        mutex_lock(&sb->s_sync_lock);
2519
2520        /*
2521         * Splice the writeback list onto a temporary list to avoid waiting on
2522         * inodes that have started writeback after this point.
2523         *
2524         * Use rcu_read_lock() to keep the inodes around until we have a
2525         * reference. s_inode_wblist_lock protects sb->s_inodes_wb as well as
2526         * the local list because inodes can be dropped from either by writeback
2527         * completion.
2528         */
2529        rcu_read_lock();
2530        spin_lock_irq(&sb->s_inode_wblist_lock);
2531        list_splice_init(&sb->s_inodes_wb, &sync_list);
2532
2533        /*
2534         * Data integrity sync. Must wait for all pages under writeback, because
2535         * there may have been pages dirtied before our sync call, but which had
2536         * writeout started before we write it out.  In which case, the inode
2537         * may not be on the dirty list, but we still have to wait for that
2538         * writeout.
2539         */
2540        while (!list_empty(&sync_list)) {
2541                struct inode *inode = list_first_entry(&sync_list, struct inode,
2542                                                       i_wb_list);
2543                struct address_space *mapping = inode->i_mapping;
2544
2545                /*
2546                 * Move each inode back to the wb list before we drop the lock
2547                 * to preserve consistency between i_wb_list and the mapping
2548                 * writeback tag. Writeback completion is responsible to remove
2549                 * the inode from either list once the writeback tag is cleared.
2550                 */
2551                list_move_tail(&inode->i_wb_list, &sb->s_inodes_wb);
2552
2553                /*
2554                 * The mapping can appear untagged while still on-list since we
2555                 * do not have the mapping lock. Skip it here, wb completion
2556                 * will remove it.
2557                 */
2558                if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))
2559                        continue;
2560
2561                spin_unlock_irq(&sb->s_inode_wblist_lock);
2562
2563                spin_lock(&inode->i_lock);
2564                if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) {
2565                        spin_unlock(&inode->i_lock);
2566
2567                        spin_lock_irq(&sb->s_inode_wblist_lock);
2568                        continue;
2569                }
2570                __iget(inode);
2571                spin_unlock(&inode->i_lock);
2572                rcu_read_unlock();
2573
2574                /*
2575                 * We keep the error status of individual mapping so that
2576                 * applications can catch the writeback error using fsync(2).
2577                 * See filemap_fdatawait_keep_errors() for details.
2578                 */
2579                filemap_fdatawait_keep_errors(mapping);
2580
2581                cond_resched();
2582
2583                iput(inode);
2584
2585                rcu_read_lock();
2586                spin_lock_irq(&sb->s_inode_wblist_lock);
2587        }
2588        spin_unlock_irq(&sb->s_inode_wblist_lock);
2589        rcu_read_unlock();
2590        mutex_unlock(&sb->s_sync_lock);
2591}
2592
2593static void __writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr,
2594                                     enum wb_reason reason, bool skip_if_busy)
2595{
2596        struct backing_dev_info *bdi = sb->s_bdi;
2597        DEFINE_WB_COMPLETION(done, bdi);
2598        struct wb_writeback_work work = {
2599                .sb                     = sb,
2600                .sync_mode              = WB_SYNC_NONE,
2601                .tagged_writepages      = 1,
2602                .done                   = &done,
2603                .nr_pages               = nr,
2604                .reason                 = reason,
2605        };
2606
2607        if (!bdi_has_dirty_io(bdi) || bdi == &noop_backing_dev_info)
2608                return;
2609        WARN_ON(!rwsem_is_locked(&sb->s_umount));
2610
2611        bdi_split_work_to_wbs(sb->s_bdi, &work, skip_if_busy);
2612        wb_wait_for_completion(&done);
2613}
2614
2615/**
2616 * writeback_inodes_sb_nr -     writeback dirty inodes from given super_block
2617 * @sb: the superblock
2618 * @nr: the number of pages to write
2619 * @reason: reason why some writeback work initiated
2620 *
2621 * Start writeback on some inodes on this super_block. No guarantees are made
2622 * on how many (if any) will be written, and this function does not wait
2623 * for IO completion of submitted IO.
2624 */
2625void writeback_inodes_sb_nr(struct super_block *sb,
2626                            unsigned long nr,
2627                            enum wb_reason reason)
2628{
2629        __writeback_inodes_sb_nr(sb, nr, reason, false);
2630}
2631EXPORT_SYMBOL(writeback_inodes_sb_nr);
2632
2633/**
2634 * writeback_inodes_sb  -       writeback dirty inodes from given super_block
2635 * @sb: the superblock
2636 * @reason: reason why some writeback work was initiated
2637 *
2638 * Start writeback on some inodes on this super_block. No guarantees are made
2639 * on how many (if any) will be written, and this function does not wait
2640 * for IO completion of submitted IO.
2641 */
2642void writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
2643{
2644        return writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
2645}
2646EXPORT_SYMBOL(writeback_inodes_sb);
2647
2648/**
2649 * try_to_writeback_inodes_sb - try to start writeback if none underway
2650 * @sb: the superblock
2651 * @reason: reason why some writeback work was initiated
2652 *
2653 * Invoke __writeback_inodes_sb_nr if no writeback is currently underway.
2654 */
2655void try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
2656{
2657        if (!down_read_trylock(&sb->s_umount))
2658                return;
2659
2660        __writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason, true);
2661        up_read(&sb->s_umount);
2662}
2663EXPORT_SYMBOL(try_to_writeback_inodes_sb);
2664
2665/**
2666 * sync_inodes_sb       -       sync sb inode pages
2667 * @sb: the superblock
2668 *
2669 * This function writes and waits on any dirty inode belonging to this
2670 * super_block.
2671 */
2672void sync_inodes_sb(struct super_block *sb)
2673{
2674        struct backing_dev_info *bdi = sb->s_bdi;
2675        DEFINE_WB_COMPLETION(done, bdi);
2676        struct wb_writeback_work work = {
2677                .sb             = sb,
2678                .sync_mode      = WB_SYNC_ALL,
2679                .nr_pages       = LONG_MAX,
2680                .range_cyclic   = 0,
2681                .done           = &done,
2682                .reason         = WB_REASON_SYNC,
2683                .for_sync       = 1,
2684        };
2685
2686        /*
2687         * Can't skip on !bdi_has_dirty() because we should wait for !dirty
2688         * inodes under writeback and I_DIRTY_TIME inodes ignored by
2689         * bdi_has_dirty() need to be written out too.
2690         */
2691        if (bdi == &noop_backing_dev_info)
2692                return;
2693        WARN_ON(!rwsem_is_locked(&sb->s_umount));
2694
2695        /* protect against inode wb switch, see inode_switch_wbs_work_fn() */
2696        bdi_down_write_wb_switch_rwsem(bdi);
2697        bdi_split_work_to_wbs(bdi, &work, false);
2698        wb_wait_for_completion(&done);
2699        bdi_up_write_wb_switch_rwsem(bdi);
2700
2701        wait_sb_inodes(sb);
2702}
2703EXPORT_SYMBOL(sync_inodes_sb);
2704
2705/**
2706 * write_inode_now      -       write an inode to disk
2707 * @inode: inode to write to disk
2708 * @sync: whether the write should be synchronous or not
2709 *
2710 * This function commits an inode to disk immediately if it is dirty. This is
2711 * primarily needed by knfsd.
2712 *
2713 * The caller must either have a ref on the inode or must have set I_WILL_FREE.
2714 */
2715int write_inode_now(struct inode *inode, int sync)
2716{
2717        struct writeback_control wbc = {
2718                .nr_to_write = LONG_MAX,
2719                .sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
2720                .range_start = 0,
2721                .range_end = LLONG_MAX,
2722        };
2723
2724        if (!mapping_can_writeback(inode->i_mapping))
2725                wbc.nr_to_write = 0;
2726
2727        might_sleep();
2728        return writeback_single_inode(inode, &wbc);
2729}
2730EXPORT_SYMBOL(write_inode_now);
2731
2732/**
2733 * sync_inode - write an inode and its pages to disk.
2734 * @inode: the inode to sync
2735 * @wbc: controls the writeback mode
2736 *
2737 * sync_inode() will write an inode and its pages to disk.  It will also
2738 * correctly update the inode on its superblock's dirty inode lists and will
2739 * update inode->i_state.
2740 *
2741 * The caller must have a ref on the inode.
2742 */
2743int sync_inode(struct inode *inode, struct writeback_control *wbc)
2744{
2745        return writeback_single_inode(inode, wbc);
2746}
2747EXPORT_SYMBOL(sync_inode);
2748
2749/**
2750 * sync_inode_metadata - write an inode to disk
2751 * @inode: the inode to sync
2752 * @wait: wait for I/O to complete.
2753 *
2754 * Write an inode to disk and adjust its dirty state after completion.
2755 *
2756 * Note: only writes the actual inode, no associated data or other metadata.
2757 */
2758int sync_inode_metadata(struct inode *inode, int wait)
2759{
2760        struct writeback_control wbc = {
2761                .sync_mode = wait ? WB_SYNC_ALL : WB_SYNC_NONE,
2762                .nr_to_write = 0, /* metadata-only */
2763        };
2764
2765        return sync_inode(inode, &wbc);
2766}
2767EXPORT_SYMBOL(sync_inode_metadata);
2768
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