linux/fs/fs-writeback.c
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   1/*
   2 * fs/fs-writeback.c
   3 *
   4 * Copyright (C) 2002, Linus Torvalds.
   5 *
   6 * Contains all the functions related to writing back and waiting
   7 * upon dirty inodes against superblocks, and writing back dirty
   8 * pages against inodes.  ie: data writeback.  Writeout of the
   9 * inode itself is not handled here.
  10 *
  11 * 10Apr2002    Andrew Morton
  12 *              Split out of fs/inode.c
  13 *              Additions for address_space-based writeback
  14 */
  15
  16#include <linux/kernel.h>
  17#include <linux/export.h>
  18#include <linux/spinlock.h>
  19#include <linux/slab.h>
  20#include <linux/sched.h>
  21#include <linux/fs.h>
  22#include <linux/mm.h>
  23#include <linux/pagemap.h>
  24#include <linux/kthread.h>
  25#include <linux/freezer.h>
  26#include <linux/writeback.h>
  27#include <linux/blkdev.h>
  28#include <linux/backing-dev.h>
  29#include <linux/tracepoint.h>
  30#include "internal.h"
  31
  32/*
  33 * 4MB minimal write chunk size
  34 */
  35#define MIN_WRITEBACK_PAGES     (4096UL >> (PAGE_CACHE_SHIFT - 10))
  36
  37/*
  38 * Passed into wb_writeback(), essentially a subset of writeback_control
  39 */
  40struct wb_writeback_work {
  41        long nr_pages;
  42        struct super_block *sb;
  43        unsigned long *older_than_this;
  44        enum writeback_sync_modes sync_mode;
  45        unsigned int tagged_writepages:1;
  46        unsigned int for_kupdate:1;
  47        unsigned int range_cyclic:1;
  48        unsigned int for_background:1;
  49        enum wb_reason reason;          /* why was writeback initiated? */
  50
  51        struct list_head list;          /* pending work list */
  52        struct completion *done;        /* set if the caller waits */
  53};
  54
  55/**
  56 * writeback_in_progress - determine whether there is writeback in progress
  57 * @bdi: the device's backing_dev_info structure.
  58 *
  59 * Determine whether there is writeback waiting to be handled against a
  60 * backing device.
  61 */
  62int writeback_in_progress(struct backing_dev_info *bdi)
  63{
  64        return test_bit(BDI_writeback_running, &bdi->state);
  65}
  66
  67static inline struct backing_dev_info *inode_to_bdi(struct inode *inode)
  68{
  69        struct super_block *sb = inode->i_sb;
  70
  71        if (strcmp(sb->s_type->name, "bdev") == 0)
  72                return inode->i_mapping->backing_dev_info;
  73
  74        return sb->s_bdi;
  75}
  76
  77static inline struct inode *wb_inode(struct list_head *head)
  78{
  79        return list_entry(head, struct inode, i_wb_list);
  80}
  81
  82/*
  83 * Include the creation of the trace points after defining the
  84 * wb_writeback_work structure and inline functions so that the definition
  85 * remains local to this file.
  86 */
  87#define CREATE_TRACE_POINTS
  88#include <trace/events/writeback.h>
  89
  90/* Wakeup flusher thread or forker thread to fork it. Requires bdi->wb_lock. */
  91static void bdi_wakeup_flusher(struct backing_dev_info *bdi)
  92{
  93        if (bdi->wb.task) {
  94                wake_up_process(bdi->wb.task);
  95        } else {
  96                /*
  97                 * The bdi thread isn't there, wake up the forker thread which
  98                 * will create and run it.
  99                 */
 100                wake_up_process(default_backing_dev_info.wb.task);
 101        }
 102}
 103
 104static void bdi_queue_work(struct backing_dev_info *bdi,
 105                           struct wb_writeback_work *work)
 106{
 107        trace_writeback_queue(bdi, work);
 108
 109        spin_lock_bh(&bdi->wb_lock);
 110        list_add_tail(&work->list, &bdi->work_list);
 111        if (!bdi->wb.task)
 112                trace_writeback_nothread(bdi, work);
 113        bdi_wakeup_flusher(bdi);
 114        spin_unlock_bh(&bdi->wb_lock);
 115}
 116
 117static void
 118__bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
 119                      bool range_cyclic, enum wb_reason reason)
 120{
 121        struct wb_writeback_work *work;
 122
 123        /*
 124         * This is WB_SYNC_NONE writeback, so if allocation fails just
 125         * wakeup the thread for old dirty data writeback
 126         */
 127        work = kzalloc(sizeof(*work), GFP_ATOMIC);
 128        if (!work) {
 129                if (bdi->wb.task) {
 130                        trace_writeback_nowork(bdi);
 131                        wake_up_process(bdi->wb.task);
 132                }
 133                return;
 134        }
 135
 136        work->sync_mode = WB_SYNC_NONE;
 137        work->nr_pages  = nr_pages;
 138        work->range_cyclic = range_cyclic;
 139        work->reason    = reason;
 140
 141        bdi_queue_work(bdi, work);
 142}
 143
 144/**
 145 * bdi_start_writeback - start writeback
 146 * @bdi: the backing device to write from
 147 * @nr_pages: the number of pages to write
 148 * @reason: reason why some writeback work was initiated
 149 *
 150 * Description:
 151 *   This does WB_SYNC_NONE opportunistic writeback. The IO is only
 152 *   started when this function returns, we make no guarantees on
 153 *   completion. Caller need not hold sb s_umount semaphore.
 154 *
 155 */
 156void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
 157                        enum wb_reason reason)
 158{
 159        __bdi_start_writeback(bdi, nr_pages, true, reason);
 160}
 161
 162/**
 163 * bdi_start_background_writeback - start background writeback
 164 * @bdi: the backing device to write from
 165 *
 166 * Description:
 167 *   This makes sure WB_SYNC_NONE background writeback happens. When
 168 *   this function returns, it is only guaranteed that for given BDI
 169 *   some IO is happening if we are over background dirty threshold.
 170 *   Caller need not hold sb s_umount semaphore.
 171 */
 172void bdi_start_background_writeback(struct backing_dev_info *bdi)
 173{
 174        /*
 175         * We just wake up the flusher thread. It will perform background
 176         * writeback as soon as there is no other work to do.
 177         */
 178        trace_writeback_wake_background(bdi);
 179        spin_lock_bh(&bdi->wb_lock);
 180        bdi_wakeup_flusher(bdi);
 181        spin_unlock_bh(&bdi->wb_lock);
 182}
 183
 184/*
 185 * Remove the inode from the writeback list it is on.
 186 */
 187void inode_wb_list_del(struct inode *inode)
 188{
 189        struct backing_dev_info *bdi = inode_to_bdi(inode);
 190
 191        spin_lock(&bdi->wb.list_lock);
 192        list_del_init(&inode->i_wb_list);
 193        spin_unlock(&bdi->wb.list_lock);
 194}
 195
 196/*
 197 * Redirty an inode: set its when-it-was dirtied timestamp and move it to the
 198 * furthest end of its superblock's dirty-inode list.
 199 *
 200 * Before stamping the inode's ->dirtied_when, we check to see whether it is
 201 * already the most-recently-dirtied inode on the b_dirty list.  If that is
 202 * the case then the inode must have been redirtied while it was being written
 203 * out and we don't reset its dirtied_when.
 204 */
 205static void redirty_tail(struct inode *inode, struct bdi_writeback *wb)
 206{
 207        assert_spin_locked(&wb->list_lock);
 208        if (!list_empty(&wb->b_dirty)) {
 209                struct inode *tail;
 210
 211                tail = wb_inode(wb->b_dirty.next);
 212                if (time_before(inode->dirtied_when, tail->dirtied_when))
 213                        inode->dirtied_when = jiffies;
 214        }
 215        list_move(&inode->i_wb_list, &wb->b_dirty);
 216}
 217
 218/*
 219 * requeue inode for re-scanning after bdi->b_io list is exhausted.
 220 */
 221static void requeue_io(struct inode *inode, struct bdi_writeback *wb)
 222{
 223        assert_spin_locked(&wb->list_lock);
 224        list_move(&inode->i_wb_list, &wb->b_more_io);
 225}
 226
 227static void inode_sync_complete(struct inode *inode)
 228{
 229        inode->i_state &= ~I_SYNC;
 230        /* Waiters must see I_SYNC cleared before being woken up */
 231        smp_mb();
 232        wake_up_bit(&inode->i_state, __I_SYNC);
 233}
 234
 235static bool inode_dirtied_after(struct inode *inode, unsigned long t)
 236{
 237        bool ret = time_after(inode->dirtied_when, t);
 238#ifndef CONFIG_64BIT
 239        /*
 240         * For inodes being constantly redirtied, dirtied_when can get stuck.
 241         * It _appears_ to be in the future, but is actually in distant past.
 242         * This test is necessary to prevent such wrapped-around relative times
 243         * from permanently stopping the whole bdi writeback.
 244         */
 245        ret = ret && time_before_eq(inode->dirtied_when, jiffies);
 246#endif
 247        return ret;
 248}
 249
 250/*
 251 * Move expired (dirtied after work->older_than_this) dirty inodes from
 252 * @delaying_queue to @dispatch_queue.
 253 */
 254static int move_expired_inodes(struct list_head *delaying_queue,
 255                               struct list_head *dispatch_queue,
 256                               struct wb_writeback_work *work)
 257{
 258        LIST_HEAD(tmp);
 259        struct list_head *pos, *node;
 260        struct super_block *sb = NULL;
 261        struct inode *inode;
 262        int do_sb_sort = 0;
 263        int moved = 0;
 264
 265        while (!list_empty(delaying_queue)) {
 266                inode = wb_inode(delaying_queue->prev);
 267                if (work->older_than_this &&
 268                    inode_dirtied_after(inode, *work->older_than_this))
 269                        break;
 270                if (sb && sb != inode->i_sb)
 271                        do_sb_sort = 1;
 272                sb = inode->i_sb;
 273                list_move(&inode->i_wb_list, &tmp);
 274                moved++;
 275        }
 276
 277        /* just one sb in list, splice to dispatch_queue and we're done */
 278        if (!do_sb_sort) {
 279                list_splice(&tmp, dispatch_queue);
 280                goto out;
 281        }
 282
 283        /* Move inodes from one superblock together */
 284        while (!list_empty(&tmp)) {
 285                sb = wb_inode(tmp.prev)->i_sb;
 286                list_for_each_prev_safe(pos, node, &tmp) {
 287                        inode = wb_inode(pos);
 288                        if (inode->i_sb == sb)
 289                                list_move(&inode->i_wb_list, dispatch_queue);
 290                }
 291        }
 292out:
 293        return moved;
 294}
 295
 296/*
 297 * Queue all expired dirty inodes for io, eldest first.
 298 * Before
 299 *         newly dirtied     b_dirty    b_io    b_more_io
 300 *         =============>    gf         edc     BA
 301 * After
 302 *         newly dirtied     b_dirty    b_io    b_more_io
 303 *         =============>    g          fBAedc
 304 *                                           |
 305 *                                           +--> dequeue for IO
 306 */
 307static void queue_io(struct bdi_writeback *wb, struct wb_writeback_work *work)
 308{
 309        int moved;
 310        assert_spin_locked(&wb->list_lock);
 311        list_splice_init(&wb->b_more_io, &wb->b_io);
 312        moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, work);
 313        trace_writeback_queue_io(wb, work, moved);
 314}
 315
 316static int write_inode(struct inode *inode, struct writeback_control *wbc)
 317{
 318        if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode))
 319                return inode->i_sb->s_op->write_inode(inode, wbc);
 320        return 0;
 321}
 322
 323/*
 324 * Wait for writeback on an inode to complete. Called with i_lock held.
 325 * Caller must make sure inode cannot go away when we drop i_lock.
 326 */
 327static void __inode_wait_for_writeback(struct inode *inode)
 328        __releases(inode->i_lock)
 329        __acquires(inode->i_lock)
 330{
 331        DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
 332        wait_queue_head_t *wqh;
 333
 334        wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
 335        while (inode->i_state & I_SYNC) {
 336                spin_unlock(&inode->i_lock);
 337                __wait_on_bit(wqh, &wq, inode_wait, TASK_UNINTERRUPTIBLE);
 338                spin_lock(&inode->i_lock);
 339        }
 340}
 341
 342/*
 343 * Wait for writeback on an inode to complete. Caller must have inode pinned.
 344 */
 345void inode_wait_for_writeback(struct inode *inode)
 346{
 347        spin_lock(&inode->i_lock);
 348        __inode_wait_for_writeback(inode);
 349        spin_unlock(&inode->i_lock);
 350}
 351
 352/*
 353 * Sleep until I_SYNC is cleared. This function must be called with i_lock
 354 * held and drops it. It is aimed for callers not holding any inode reference
 355 * so once i_lock is dropped, inode can go away.
 356 */
 357static void inode_sleep_on_writeback(struct inode *inode)
 358        __releases(inode->i_lock)
 359{
 360        DEFINE_WAIT(wait);
 361        wait_queue_head_t *wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
 362        int sleep;
 363
 364        prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
 365        sleep = inode->i_state & I_SYNC;
 366        spin_unlock(&inode->i_lock);
 367        if (sleep)
 368                schedule();
 369        finish_wait(wqh, &wait);
 370}
 371
 372/*
 373 * Find proper writeback list for the inode depending on its current state and
 374 * possibly also change of its state while we were doing writeback.  Here we
 375 * handle things such as livelock prevention or fairness of writeback among
 376 * inodes. This function can be called only by flusher thread - noone else
 377 * processes all inodes in writeback lists and requeueing inodes behind flusher
 378 * thread's back can have unexpected consequences.
 379 */
 380static void requeue_inode(struct inode *inode, struct bdi_writeback *wb,
 381                          struct writeback_control *wbc)
 382{
 383        if (inode->i_state & I_FREEING)
 384                return;
 385
 386        /*
 387         * Sync livelock prevention. Each inode is tagged and synced in one
 388         * shot. If still dirty, it will be redirty_tail()'ed below.  Update
 389         * the dirty time to prevent enqueue and sync it again.
 390         */
 391        if ((inode->i_state & I_DIRTY) &&
 392            (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages))
 393                inode->dirtied_when = jiffies;
 394
 395        if (wbc->pages_skipped) {
 396                /*
 397                 * writeback is not making progress due to locked
 398                 * buffers. Skip this inode for now.
 399                 */
 400                redirty_tail(inode, wb);
 401                return;
 402        }
 403
 404        if (mapping_tagged(inode->i_mapping, PAGECACHE_TAG_DIRTY)) {
 405                /*
 406                 * We didn't write back all the pages.  nfs_writepages()
 407                 * sometimes bales out without doing anything.
 408                 */
 409                if (wbc->nr_to_write <= 0) {
 410                        /* Slice used up. Queue for next turn. */
 411                        requeue_io(inode, wb);
 412                } else {
 413                        /*
 414                         * Writeback blocked by something other than
 415                         * congestion. Delay the inode for some time to
 416                         * avoid spinning on the CPU (100% iowait)
 417                         * retrying writeback of the dirty page/inode
 418                         * that cannot be performed immediately.
 419                         */
 420                        redirty_tail(inode, wb);
 421                }
 422        } else if (inode->i_state & I_DIRTY) {
 423                /*
 424                 * Filesystems can dirty the inode during writeback operations,
 425                 * such as delayed allocation during submission or metadata
 426                 * updates after data IO completion.
 427                 */
 428                redirty_tail(inode, wb);
 429        } else {
 430                /* The inode is clean. Remove from writeback lists. */
 431                list_del_init(&inode->i_wb_list);
 432        }
 433}
 434
 435/*
 436 * Write out an inode and its dirty pages. Do not update the writeback list
 437 * linkage. That is left to the caller. The caller is also responsible for
 438 * setting I_SYNC flag and calling inode_sync_complete() to clear it.
 439 */
 440static int
 441__writeback_single_inode(struct inode *inode, struct bdi_writeback *wb,
 442                         struct writeback_control *wbc)
 443{
 444        struct address_space *mapping = inode->i_mapping;
 445        long nr_to_write = wbc->nr_to_write;
 446        unsigned dirty;
 447        int ret;
 448
 449        WARN_ON(!(inode->i_state & I_SYNC));
 450
 451        ret = do_writepages(mapping, wbc);
 452
 453        /*
 454         * Make sure to wait on the data before writing out the metadata.
 455         * This is important for filesystems that modify metadata on data
 456         * I/O completion.
 457         */
 458        if (wbc->sync_mode == WB_SYNC_ALL) {
 459                int err = filemap_fdatawait(mapping);
 460                if (ret == 0)
 461                        ret = err;
 462        }
 463
 464        /*
 465         * Some filesystems may redirty the inode during the writeback
 466         * due to delalloc, clear dirty metadata flags right before
 467         * write_inode()
 468         */
 469        spin_lock(&inode->i_lock);
 470        /* Clear I_DIRTY_PAGES if we've written out all dirty pages */
 471        if (!mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
 472                inode->i_state &= ~I_DIRTY_PAGES;
 473        dirty = inode->i_state & I_DIRTY;
 474        inode->i_state &= ~(I_DIRTY_SYNC | I_DIRTY_DATASYNC);
 475        spin_unlock(&inode->i_lock);
 476        /* Don't write the inode if only I_DIRTY_PAGES was set */
 477        if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
 478                int err = write_inode(inode, wbc);
 479                if (ret == 0)
 480                        ret = err;
 481        }
 482        trace_writeback_single_inode(inode, wbc, nr_to_write);
 483        return ret;
 484}
 485
 486/*
 487 * Write out an inode's dirty pages. Either the caller has an active reference
 488 * on the inode or the inode has I_WILL_FREE set.
 489 *
 490 * This function is designed to be called for writing back one inode which
 491 * we go e.g. from filesystem. Flusher thread uses __writeback_single_inode()
 492 * and does more profound writeback list handling in writeback_sb_inodes().
 493 */
 494static int
 495writeback_single_inode(struct inode *inode, struct bdi_writeback *wb,
 496                       struct writeback_control *wbc)
 497{
 498        int ret = 0;
 499
 500        spin_lock(&inode->i_lock);
 501        if (!atomic_read(&inode->i_count))
 502                WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
 503        else
 504                WARN_ON(inode->i_state & I_WILL_FREE);
 505
 506        if (inode->i_state & I_SYNC) {
 507                if (wbc->sync_mode != WB_SYNC_ALL)
 508                        goto out;
 509                /*
 510                 * It's a data-integrity sync. We must wait. Since callers hold
 511                 * inode reference or inode has I_WILL_FREE set, it cannot go
 512                 * away under us.
 513                 */
 514                __inode_wait_for_writeback(inode);
 515        }
 516        WARN_ON(inode->i_state & I_SYNC);
 517        /*
 518         * Skip inode if it is clean. We don't want to mess with writeback
 519         * lists in this function since flusher thread may be doing for example
 520         * sync in parallel and if we move the inode, it could get skipped. So
 521         * here we make sure inode is on some writeback list and leave it there
 522         * unless we have completely cleaned the inode.
 523         */
 524        if (!(inode->i_state & I_DIRTY))
 525                goto out;
 526        inode->i_state |= I_SYNC;
 527        spin_unlock(&inode->i_lock);
 528
 529        ret = __writeback_single_inode(inode, wb, wbc);
 530
 531        spin_lock(&wb->list_lock);
 532        spin_lock(&inode->i_lock);
 533        /*
 534         * If inode is clean, remove it from writeback lists. Otherwise don't
 535         * touch it. See comment above for explanation.
 536         */
 537        if (!(inode->i_state & I_DIRTY))
 538                list_del_init(&inode->i_wb_list);
 539        spin_unlock(&wb->list_lock);
 540        inode_sync_complete(inode);
 541out:
 542        spin_unlock(&inode->i_lock);
 543        return ret;
 544}
 545
 546static long writeback_chunk_size(struct backing_dev_info *bdi,
 547                                 struct wb_writeback_work *work)
 548{
 549        long pages;
 550
 551        /*
 552         * WB_SYNC_ALL mode does livelock avoidance by syncing dirty
 553         * inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
 554         * here avoids calling into writeback_inodes_wb() more than once.
 555         *
 556         * The intended call sequence for WB_SYNC_ALL writeback is:
 557         *
 558         *      wb_writeback()
 559         *          writeback_sb_inodes()       <== called only once
 560         *              write_cache_pages()     <== called once for each inode
 561         *                   (quickly) tag currently dirty pages
 562         *                   (maybe slowly) sync all tagged pages
 563         */
 564        if (work->sync_mode == WB_SYNC_ALL || work->tagged_writepages)
 565                pages = LONG_MAX;
 566        else {
 567                pages = min(bdi->avg_write_bandwidth / 2,
 568                            global_dirty_limit / DIRTY_SCOPE);
 569                pages = min(pages, work->nr_pages);
 570                pages = round_down(pages + MIN_WRITEBACK_PAGES,
 571                                   MIN_WRITEBACK_PAGES);
 572        }
 573
 574        return pages;
 575}
 576
 577/*
 578 * Write a portion of b_io inodes which belong to @sb.
 579 *
 580 * If @only_this_sb is true, then find and write all such
 581 * inodes. Otherwise write only ones which go sequentially
 582 * in reverse order.
 583 *
 584 * Return the number of pages and/or inodes written.
 585 */
 586static long writeback_sb_inodes(struct super_block *sb,
 587                                struct bdi_writeback *wb,
 588                                struct wb_writeback_work *work)
 589{
 590        struct writeback_control wbc = {
 591                .sync_mode              = work->sync_mode,
 592                .tagged_writepages      = work->tagged_writepages,
 593                .for_kupdate            = work->for_kupdate,
 594                .for_background         = work->for_background,
 595                .range_cyclic           = work->range_cyclic,
 596                .range_start            = 0,
 597                .range_end              = LLONG_MAX,
 598        };
 599        unsigned long start_time = jiffies;
 600        long write_chunk;
 601        long wrote = 0;  /* count both pages and inodes */
 602
 603        while (!list_empty(&wb->b_io)) {
 604                struct inode *inode = wb_inode(wb->b_io.prev);
 605
 606                if (inode->i_sb != sb) {
 607                        if (work->sb) {
 608                                /*
 609                                 * We only want to write back data for this
 610                                 * superblock, move all inodes not belonging
 611                                 * to it back onto the dirty list.
 612                                 */
 613                                redirty_tail(inode, wb);
 614                                continue;
 615                        }
 616
 617                        /*
 618                         * The inode belongs to a different superblock.
 619                         * Bounce back to the caller to unpin this and
 620                         * pin the next superblock.
 621                         */
 622                        break;
 623                }
 624
 625                /*
 626                 * Don't bother with new inodes or inodes being freed, first
 627                 * kind does not need periodic writeout yet, and for the latter
 628                 * kind writeout is handled by the freer.
 629                 */
 630                spin_lock(&inode->i_lock);
 631                if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
 632                        spin_unlock(&inode->i_lock);
 633                        redirty_tail(inode, wb);
 634                        continue;
 635                }
 636                if ((inode->i_state & I_SYNC) && wbc.sync_mode != WB_SYNC_ALL) {
 637                        /*
 638                         * If this inode is locked for writeback and we are not
 639                         * doing writeback-for-data-integrity, move it to
 640                         * b_more_io so that writeback can proceed with the
 641                         * other inodes on s_io.
 642                         *
 643                         * We'll have another go at writing back this inode
 644                         * when we completed a full scan of b_io.
 645                         */
 646                        spin_unlock(&inode->i_lock);
 647                        requeue_io(inode, wb);
 648                        trace_writeback_sb_inodes_requeue(inode);
 649                        continue;
 650                }
 651                spin_unlock(&wb->list_lock);
 652
 653                /*
 654                 * We already requeued the inode if it had I_SYNC set and we
 655                 * are doing WB_SYNC_NONE writeback. So this catches only the
 656                 * WB_SYNC_ALL case.
 657                 */
 658                if (inode->i_state & I_SYNC) {
 659                        /* Wait for I_SYNC. This function drops i_lock... */
 660                        inode_sleep_on_writeback(inode);
 661                        /* Inode may be gone, start again */
 662                        spin_lock(&wb->list_lock);
 663                        continue;
 664                }
 665                inode->i_state |= I_SYNC;
 666                spin_unlock(&inode->i_lock);
 667
 668                write_chunk = writeback_chunk_size(wb->bdi, work);
 669                wbc.nr_to_write = write_chunk;
 670                wbc.pages_skipped = 0;
 671
 672                /*
 673                 * We use I_SYNC to pin the inode in memory. While it is set
 674                 * evict_inode() will wait so the inode cannot be freed.
 675                 */
 676                __writeback_single_inode(inode, wb, &wbc);
 677
 678                work->nr_pages -= write_chunk - wbc.nr_to_write;
 679                wrote += write_chunk - wbc.nr_to_write;
 680                spin_lock(&wb->list_lock);
 681                spin_lock(&inode->i_lock);
 682                if (!(inode->i_state & I_DIRTY))
 683                        wrote++;
 684                requeue_inode(inode, wb, &wbc);
 685                inode_sync_complete(inode);
 686                spin_unlock(&inode->i_lock);
 687                cond_resched_lock(&wb->list_lock);
 688                /*
 689                 * bail out to wb_writeback() often enough to check
 690                 * background threshold and other termination conditions.
 691                 */
 692                if (wrote) {
 693                        if (time_is_before_jiffies(start_time + HZ / 10UL))
 694                                break;
 695                        if (work->nr_pages <= 0)
 696                                break;
 697                }
 698        }
 699        return wrote;
 700}
 701
 702static long __writeback_inodes_wb(struct bdi_writeback *wb,
 703                                  struct wb_writeback_work *work)
 704{
 705        unsigned long start_time = jiffies;
 706        long wrote = 0;
 707
 708        while (!list_empty(&wb->b_io)) {
 709                struct inode *inode = wb_inode(wb->b_io.prev);
 710                struct super_block *sb = inode->i_sb;
 711
 712                if (!grab_super_passive(sb)) {
 713                        /*
 714                         * grab_super_passive() may fail consistently due to
 715                         * s_umount being grabbed by someone else. Don't use
 716                         * requeue_io() to avoid busy retrying the inode/sb.
 717                         */
 718                        redirty_tail(inode, wb);
 719                        continue;
 720                }
 721                wrote += writeback_sb_inodes(sb, wb, work);
 722                drop_super(sb);
 723
 724                /* refer to the same tests at the end of writeback_sb_inodes */
 725                if (wrote) {
 726                        if (time_is_before_jiffies(start_time + HZ / 10UL))
 727                                break;
 728                        if (work->nr_pages <= 0)
 729                                break;
 730                }
 731        }
 732        /* Leave any unwritten inodes on b_io */
 733        return wrote;
 734}
 735
 736long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
 737                                enum wb_reason reason)
 738{
 739        struct wb_writeback_work work = {
 740                .nr_pages       = nr_pages,
 741                .sync_mode      = WB_SYNC_NONE,
 742                .range_cyclic   = 1,
 743                .reason         = reason,
 744        };
 745
 746        spin_lock(&wb->list_lock);
 747        if (list_empty(&wb->b_io))
 748                queue_io(wb, &work);
 749        __writeback_inodes_wb(wb, &work);
 750        spin_unlock(&wb->list_lock);
 751
 752        return nr_pages - work.nr_pages;
 753}
 754
 755static bool over_bground_thresh(struct backing_dev_info *bdi)
 756{
 757        unsigned long background_thresh, dirty_thresh;
 758
 759        global_dirty_limits(&background_thresh, &dirty_thresh);
 760
 761        if (global_page_state(NR_FILE_DIRTY) +
 762            global_page_state(NR_UNSTABLE_NFS) > background_thresh)
 763                return true;
 764
 765        if (bdi_stat(bdi, BDI_RECLAIMABLE) >
 766                                bdi_dirty_limit(bdi, background_thresh))
 767                return true;
 768
 769        return false;
 770}
 771
 772/*
 773 * Called under wb->list_lock. If there are multiple wb per bdi,
 774 * only the flusher working on the first wb should do it.
 775 */
 776static void wb_update_bandwidth(struct bdi_writeback *wb,
 777                                unsigned long start_time)
 778{
 779        __bdi_update_bandwidth(wb->bdi, 0, 0, 0, 0, 0, start_time);
 780}
 781
 782/*
 783 * Explicit flushing or periodic writeback of "old" data.
 784 *
 785 * Define "old": the first time one of an inode's pages is dirtied, we mark the
 786 * dirtying-time in the inode's address_space.  So this periodic writeback code
 787 * just walks the superblock inode list, writing back any inodes which are
 788 * older than a specific point in time.
 789 *
 790 * Try to run once per dirty_writeback_interval.  But if a writeback event
 791 * takes longer than a dirty_writeback_interval interval, then leave a
 792 * one-second gap.
 793 *
 794 * older_than_this takes precedence over nr_to_write.  So we'll only write back
 795 * all dirty pages if they are all attached to "old" mappings.
 796 */
 797static long wb_writeback(struct bdi_writeback *wb,
 798                         struct wb_writeback_work *work)
 799{
 800        unsigned long wb_start = jiffies;
 801        long nr_pages = work->nr_pages;
 802        unsigned long oldest_jif;
 803        struct inode *inode;
 804        long progress;
 805
 806        oldest_jif = jiffies;
 807        work->older_than_this = &oldest_jif;
 808
 809        spin_lock(&wb->list_lock);
 810        for (;;) {
 811                /*
 812                 * Stop writeback when nr_pages has been consumed
 813                 */
 814                if (work->nr_pages <= 0)
 815                        break;
 816
 817                /*
 818                 * Background writeout and kupdate-style writeback may
 819                 * run forever. Stop them if there is other work to do
 820                 * so that e.g. sync can proceed. They'll be restarted
 821                 * after the other works are all done.
 822                 */
 823                if ((work->for_background || work->for_kupdate) &&
 824                    !list_empty(&wb->bdi->work_list))
 825                        break;
 826
 827                /*
 828                 * For background writeout, stop when we are below the
 829                 * background dirty threshold
 830                 */
 831                if (work->for_background && !over_bground_thresh(wb->bdi))
 832                        break;
 833
 834                /*
 835                 * Kupdate and background works are special and we want to
 836                 * include all inodes that need writing. Livelock avoidance is
 837                 * handled by these works yielding to any other work so we are
 838                 * safe.
 839                 */
 840                if (work->for_kupdate) {
 841                        oldest_jif = jiffies -
 842                                msecs_to_jiffies(dirty_expire_interval * 10);
 843                } else if (work->for_background)
 844                        oldest_jif = jiffies;
 845
 846                trace_writeback_start(wb->bdi, work);
 847                if (list_empty(&wb->b_io))
 848                        queue_io(wb, work);
 849                if (work->sb)
 850                        progress = writeback_sb_inodes(work->sb, wb, work);
 851                else
 852                        progress = __writeback_inodes_wb(wb, work);
 853                trace_writeback_written(wb->bdi, work);
 854
 855                wb_update_bandwidth(wb, wb_start);
 856
 857                /*
 858                 * Did we write something? Try for more
 859                 *
 860                 * Dirty inodes are moved to b_io for writeback in batches.
 861                 * The completion of the current batch does not necessarily
 862                 * mean the overall work is done. So we keep looping as long
 863                 * as made some progress on cleaning pages or inodes.
 864                 */
 865                if (progress)
 866                        continue;
 867                /*
 868                 * No more inodes for IO, bail
 869                 */
 870                if (list_empty(&wb->b_more_io))
 871                        break;
 872                /*
 873                 * Nothing written. Wait for some inode to
 874                 * become available for writeback. Otherwise
 875                 * we'll just busyloop.
 876                 */
 877                if (!list_empty(&wb->b_more_io))  {
 878                        trace_writeback_wait(wb->bdi, work);
 879                        inode = wb_inode(wb->b_more_io.prev);
 880                        spin_lock(&inode->i_lock);
 881                        spin_unlock(&wb->list_lock);
 882                        /* This function drops i_lock... */
 883                        inode_sleep_on_writeback(inode);
 884                        spin_lock(&wb->list_lock);
 885                }
 886        }
 887        spin_unlock(&wb->list_lock);
 888
 889        return nr_pages - work->nr_pages;
 890}
 891
 892/*
 893 * Return the next wb_writeback_work struct that hasn't been processed yet.
 894 */
 895static struct wb_writeback_work *
 896get_next_work_item(struct backing_dev_info *bdi)
 897{
 898        struct wb_writeback_work *work = NULL;
 899
 900        spin_lock_bh(&bdi->wb_lock);
 901        if (!list_empty(&bdi->work_list)) {
 902                work = list_entry(bdi->work_list.next,
 903                                  struct wb_writeback_work, list);
 904                list_del_init(&work->list);
 905        }
 906        spin_unlock_bh(&bdi->wb_lock);
 907        return work;
 908}
 909
 910/*
 911 * Add in the number of potentially dirty inodes, because each inode
 912 * write can dirty pagecache in the underlying blockdev.
 913 */
 914static unsigned long get_nr_dirty_pages(void)
 915{
 916        return global_page_state(NR_FILE_DIRTY) +
 917                global_page_state(NR_UNSTABLE_NFS) +
 918                get_nr_dirty_inodes();
 919}
 920
 921static long wb_check_background_flush(struct bdi_writeback *wb)
 922{
 923        if (over_bground_thresh(wb->bdi)) {
 924
 925                struct wb_writeback_work work = {
 926                        .nr_pages       = LONG_MAX,
 927                        .sync_mode      = WB_SYNC_NONE,
 928                        .for_background = 1,
 929                        .range_cyclic   = 1,
 930                        .reason         = WB_REASON_BACKGROUND,
 931                };
 932
 933                return wb_writeback(wb, &work);
 934        }
 935
 936        return 0;
 937}
 938
 939static long wb_check_old_data_flush(struct bdi_writeback *wb)
 940{
 941        unsigned long expired;
 942        long nr_pages;
 943
 944        /*
 945         * When set to zero, disable periodic writeback
 946         */
 947        if (!dirty_writeback_interval)
 948                return 0;
 949
 950        expired = wb->last_old_flush +
 951                        msecs_to_jiffies(dirty_writeback_interval * 10);
 952        if (time_before(jiffies, expired))
 953                return 0;
 954
 955        wb->last_old_flush = jiffies;
 956        nr_pages = get_nr_dirty_pages();
 957
 958        if (nr_pages) {
 959                struct wb_writeback_work work = {
 960                        .nr_pages       = nr_pages,
 961                        .sync_mode      = WB_SYNC_NONE,
 962                        .for_kupdate    = 1,
 963                        .range_cyclic   = 1,
 964                        .reason         = WB_REASON_PERIODIC,
 965                };
 966
 967                return wb_writeback(wb, &work);
 968        }
 969
 970        return 0;
 971}
 972
 973/*
 974 * Retrieve work items and do the writeback they describe
 975 */
 976long wb_do_writeback(struct bdi_writeback *wb, int force_wait)
 977{
 978        struct backing_dev_info *bdi = wb->bdi;
 979        struct wb_writeback_work *work;
 980        long wrote = 0;
 981
 982        set_bit(BDI_writeback_running, &wb->bdi->state);
 983        while ((work = get_next_work_item(bdi)) != NULL) {
 984                /*
 985                 * Override sync mode, in case we must wait for completion
 986                 * because this thread is exiting now.
 987                 */
 988                if (force_wait)
 989                        work->sync_mode = WB_SYNC_ALL;
 990
 991                trace_writeback_exec(bdi, work);
 992
 993                wrote += wb_writeback(wb, work);
 994
 995                /*
 996                 * Notify the caller of completion if this is a synchronous
 997                 * work item, otherwise just free it.
 998                 */
 999                if (work->done)
1000                        complete(work->done);
1001                else
1002                        kfree(work);
1003        }
1004
1005        /*
1006         * Check for periodic writeback, kupdated() style
1007         */
1008        wrote += wb_check_old_data_flush(wb);
1009        wrote += wb_check_background_flush(wb);
1010        clear_bit(BDI_writeback_running, &wb->bdi->state);
1011
1012        return wrote;
1013}
1014
1015/*
1016 * Handle writeback of dirty data for the device backed by this bdi. Also
1017 * wakes up periodically and does kupdated style flushing.
1018 */
1019int bdi_writeback_thread(void *data)
1020{
1021        struct bdi_writeback *wb = data;
1022        struct backing_dev_info *bdi = wb->bdi;
1023        long pages_written;
1024
1025        current->flags |= PF_SWAPWRITE;
1026        set_freezable();
1027        wb->last_active = jiffies;
1028
1029        /*
1030         * Our parent may run at a different priority, just set us to normal
1031         */
1032        set_user_nice(current, 0);
1033
1034        trace_writeback_thread_start(bdi);
1035
1036        while (!kthread_freezable_should_stop(NULL)) {
1037                /*
1038                 * Remove own delayed wake-up timer, since we are already awake
1039                 * and we'll take care of the preriodic write-back.
1040                 */
1041                del_timer(&wb->wakeup_timer);
1042
1043                pages_written = wb_do_writeback(wb, 0);
1044
1045                trace_writeback_pages_written(pages_written);
1046
1047                if (pages_written)
1048                        wb->last_active = jiffies;
1049
1050                set_current_state(TASK_INTERRUPTIBLE);
1051                if (!list_empty(&bdi->work_list) || kthread_should_stop()) {
1052                        __set_current_state(TASK_RUNNING);
1053                        continue;
1054                }
1055
1056                if (wb_has_dirty_io(wb) && dirty_writeback_interval)
1057                        schedule_timeout(msecs_to_jiffies(dirty_writeback_interval * 10));
1058                else {
1059                        /*
1060                         * We have nothing to do, so can go sleep without any
1061                         * timeout and save power. When a work is queued or
1062                         * something is made dirty - we will be woken up.
1063                         */
1064                        schedule();
1065                }
1066        }
1067
1068        /* Flush any work that raced with us exiting */
1069        if (!list_empty(&bdi->work_list))
1070                wb_do_writeback(wb, 1);
1071
1072        trace_writeback_thread_stop(bdi);
1073        return 0;
1074}
1075
1076
1077/*
1078 * Start writeback of `nr_pages' pages.  If `nr_pages' is zero, write back
1079 * the whole world.
1080 */
1081void wakeup_flusher_threads(long nr_pages, enum wb_reason reason)
1082{
1083        struct backing_dev_info *bdi;
1084
1085        if (!nr_pages) {
1086                nr_pages = global_page_state(NR_FILE_DIRTY) +
1087                                global_page_state(NR_UNSTABLE_NFS);
1088        }
1089
1090        rcu_read_lock();
1091        list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
1092                if (!bdi_has_dirty_io(bdi))
1093                        continue;
1094                __bdi_start_writeback(bdi, nr_pages, false, reason);
1095        }
1096        rcu_read_unlock();
1097}
1098
1099static noinline void block_dump___mark_inode_dirty(struct inode *inode)
1100{
1101        if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) {
1102                struct dentry *dentry;
1103                const char *name = "?";
1104
1105                dentry = d_find_alias(inode);
1106                if (dentry) {
1107                        spin_lock(&dentry->d_lock);
1108                        name = (const char *) dentry->d_name.name;
1109                }
1110                printk(KERN_DEBUG
1111                       "%s(%d): dirtied inode %lu (%s) on %s\n",
1112                       current->comm, task_pid_nr(current), inode->i_ino,
1113                       name, inode->i_sb->s_id);
1114                if (dentry) {
1115                        spin_unlock(&dentry->d_lock);
1116                        dput(dentry);
1117                }
1118        }
1119}
1120
1121/**
1122 *      __mark_inode_dirty -    internal function
1123 *      @inode: inode to mark
1124 *      @flags: what kind of dirty (i.e. I_DIRTY_SYNC)
1125 *      Mark an inode as dirty. Callers should use mark_inode_dirty or
1126 *      mark_inode_dirty_sync.
1127 *
1128 * Put the inode on the super block's dirty list.
1129 *
1130 * CAREFUL! We mark it dirty unconditionally, but move it onto the
1131 * dirty list only if it is hashed or if it refers to a blockdev.
1132 * If it was not hashed, it will never be added to the dirty list
1133 * even if it is later hashed, as it will have been marked dirty already.
1134 *
1135 * In short, make sure you hash any inodes _before_ you start marking
1136 * them dirty.
1137 *
1138 * Note that for blockdevs, inode->dirtied_when represents the dirtying time of
1139 * the block-special inode (/dev/hda1) itself.  And the ->dirtied_when field of
1140 * the kernel-internal blockdev inode represents the dirtying time of the
1141 * blockdev's pages.  This is why for I_DIRTY_PAGES we always use
1142 * page->mapping->host, so the page-dirtying time is recorded in the internal
1143 * blockdev inode.
1144 */
1145void __mark_inode_dirty(struct inode *inode, int flags)
1146{
1147        struct super_block *sb = inode->i_sb;
1148        struct backing_dev_info *bdi = NULL;
1149
1150        /*
1151         * Don't do this for I_DIRTY_PAGES - that doesn't actually
1152         * dirty the inode itself
1153         */
1154        if (flags & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
1155                if (sb->s_op->dirty_inode)
1156                        sb->s_op->dirty_inode(inode, flags);
1157        }
1158
1159        /*
1160         * make sure that changes are seen by all cpus before we test i_state
1161         * -- mikulas
1162         */
1163        smp_mb();
1164
1165        /* avoid the locking if we can */
1166        if ((inode->i_state & flags) == flags)
1167                return;
1168
1169        if (unlikely(block_dump))
1170                block_dump___mark_inode_dirty(inode);
1171
1172        spin_lock(&inode->i_lock);
1173        if ((inode->i_state & flags) != flags) {
1174                const int was_dirty = inode->i_state & I_DIRTY;
1175
1176                inode->i_state |= flags;
1177
1178                /*
1179                 * If the inode is being synced, just update its dirty state.
1180                 * The unlocker will place the inode on the appropriate
1181                 * superblock list, based upon its state.
1182                 */
1183                if (inode->i_state & I_SYNC)
1184                        goto out_unlock_inode;
1185
1186                /*
1187                 * Only add valid (hashed) inodes to the superblock's
1188                 * dirty list.  Add blockdev inodes as well.
1189                 */
1190                if (!S_ISBLK(inode->i_mode)) {
1191                        if (inode_unhashed(inode))
1192                                goto out_unlock_inode;
1193                }
1194                if (inode->i_state & I_FREEING)
1195                        goto out_unlock_inode;
1196
1197                /*
1198                 * If the inode was already on b_dirty/b_io/b_more_io, don't
1199                 * reposition it (that would break b_dirty time-ordering).
1200                 */
1201                if (!was_dirty) {
1202                        bool wakeup_bdi = false;
1203                        bdi = inode_to_bdi(inode);
1204
1205                        if (bdi_cap_writeback_dirty(bdi)) {
1206                                WARN(!test_bit(BDI_registered, &bdi->state),
1207                                     "bdi-%s not registered\n", bdi->name);
1208
1209                                /*
1210                                 * If this is the first dirty inode for this
1211                                 * bdi, we have to wake-up the corresponding
1212                                 * bdi thread to make sure background
1213                                 * write-back happens later.
1214                                 */
1215                                if (!wb_has_dirty_io(&bdi->wb))
1216                                        wakeup_bdi = true;
1217                        }
1218
1219                        spin_unlock(&inode->i_lock);
1220                        spin_lock(&bdi->wb.list_lock);
1221                        inode->dirtied_when = jiffies;
1222                        list_move(&inode->i_wb_list, &bdi->wb.b_dirty);
1223                        spin_unlock(&bdi->wb.list_lock);
1224
1225                        if (wakeup_bdi)
1226                                bdi_wakeup_thread_delayed(bdi);
1227                        return;
1228                }
1229        }
1230out_unlock_inode:
1231        spin_unlock(&inode->i_lock);
1232
1233}
1234EXPORT_SYMBOL(__mark_inode_dirty);
1235
1236static void wait_sb_inodes(struct super_block *sb)
1237{
1238        struct inode *inode, *old_inode = NULL;
1239
1240        /*
1241         * We need to be protected against the filesystem going from
1242         * r/o to r/w or vice versa.
1243         */
1244        WARN_ON(!rwsem_is_locked(&sb->s_umount));
1245
1246        spin_lock(&inode_sb_list_lock);
1247
1248        /*
1249         * Data integrity sync. Must wait for all pages under writeback,
1250         * because there may have been pages dirtied before our sync
1251         * call, but which had writeout started before we write it out.
1252         * In which case, the inode may not be on the dirty list, but
1253         * we still have to wait for that writeout.
1254         */
1255        list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
1256                struct address_space *mapping = inode->i_mapping;
1257
1258                spin_lock(&inode->i_lock);
1259                if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
1260                    (mapping->nrpages == 0)) {
1261                        spin_unlock(&inode->i_lock);
1262                        continue;
1263                }
1264                __iget(inode);
1265                spin_unlock(&inode->i_lock);
1266                spin_unlock(&inode_sb_list_lock);
1267
1268                /*
1269                 * We hold a reference to 'inode' so it couldn't have been
1270                 * removed from s_inodes list while we dropped the
1271                 * inode_sb_list_lock.  We cannot iput the inode now as we can
1272                 * be holding the last reference and we cannot iput it under
1273                 * inode_sb_list_lock. So we keep the reference and iput it
1274                 * later.
1275                 */
1276                iput(old_inode);
1277                old_inode = inode;
1278
1279                filemap_fdatawait(mapping);
1280
1281                cond_resched();
1282
1283                spin_lock(&inode_sb_list_lock);
1284        }
1285        spin_unlock(&inode_sb_list_lock);
1286        iput(old_inode);
1287}
1288
1289/**
1290 * writeback_inodes_sb_nr -     writeback dirty inodes from given super_block
1291 * @sb: the superblock
1292 * @nr: the number of pages to write
1293 * @reason: reason why some writeback work initiated
1294 *
1295 * Start writeback on some inodes on this super_block. No guarantees are made
1296 * on how many (if any) will be written, and this function does not wait
1297 * for IO completion of submitted IO.
1298 */
1299void writeback_inodes_sb_nr(struct super_block *sb,
1300                            unsigned long nr,
1301                            enum wb_reason reason)
1302{
1303        DECLARE_COMPLETION_ONSTACK(done);
1304        struct wb_writeback_work work = {
1305                .sb                     = sb,
1306                .sync_mode              = WB_SYNC_NONE,
1307                .tagged_writepages      = 1,
1308                .done                   = &done,
1309                .nr_pages               = nr,
1310                .reason                 = reason,
1311        };
1312
1313        if (sb->s_bdi == &noop_backing_dev_info)
1314                return;
1315        WARN_ON(!rwsem_is_locked(&sb->s_umount));
1316        bdi_queue_work(sb->s_bdi, &work);
1317        wait_for_completion(&done);
1318}
1319EXPORT_SYMBOL(writeback_inodes_sb_nr);
1320
1321/**
1322 * writeback_inodes_sb  -       writeback dirty inodes from given super_block
1323 * @sb: the superblock
1324 * @reason: reason why some writeback work was initiated
1325 *
1326 * Start writeback on some inodes on this super_block. No guarantees are made
1327 * on how many (if any) will be written, and this function does not wait
1328 * for IO completion of submitted IO.
1329 */
1330void writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
1331{
1332        return writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
1333}
1334EXPORT_SYMBOL(writeback_inodes_sb);
1335
1336/**
1337 * writeback_inodes_sb_if_idle  -       start writeback if none underway
1338 * @sb: the superblock
1339 * @reason: reason why some writeback work was initiated
1340 *
1341 * Invoke writeback_inodes_sb if no writeback is currently underway.
1342 * Returns 1 if writeback was started, 0 if not.
1343 */
1344int writeback_inodes_sb_if_idle(struct super_block *sb, enum wb_reason reason)
1345{
1346        if (!writeback_in_progress(sb->s_bdi)) {
1347                down_read(&sb->s_umount);
1348                writeback_inodes_sb(sb, reason);
1349                up_read(&sb->s_umount);
1350                return 1;
1351        } else
1352                return 0;
1353}
1354EXPORT_SYMBOL(writeback_inodes_sb_if_idle);
1355
1356/**
1357 * writeback_inodes_sb_nr_if_idle       -       start writeback if none underway
1358 * @sb: the superblock
1359 * @nr: the number of pages to write
1360 * @reason: reason why some writeback work was initiated
1361 *
1362 * Invoke writeback_inodes_sb if no writeback is currently underway.
1363 * Returns 1 if writeback was started, 0 if not.
1364 */
1365int writeback_inodes_sb_nr_if_idle(struct super_block *sb,
1366                                   unsigned long nr,
1367                                   enum wb_reason reason)
1368{
1369        if (!writeback_in_progress(sb->s_bdi)) {
1370                down_read(&sb->s_umount);
1371                writeback_inodes_sb_nr(sb, nr, reason);
1372                up_read(&sb->s_umount);
1373                return 1;
1374        } else
1375                return 0;
1376}
1377EXPORT_SYMBOL(writeback_inodes_sb_nr_if_idle);
1378
1379/**
1380 * sync_inodes_sb       -       sync sb inode pages
1381 * @sb: the superblock
1382 *
1383 * This function writes and waits on any dirty inode belonging to this
1384 * super_block.
1385 */
1386void sync_inodes_sb(struct super_block *sb)
1387{
1388        DECLARE_COMPLETION_ONSTACK(done);
1389        struct wb_writeback_work work = {
1390                .sb             = sb,
1391                .sync_mode      = WB_SYNC_ALL,
1392                .nr_pages       = LONG_MAX,
1393                .range_cyclic   = 0,
1394                .done           = &done,
1395                .reason         = WB_REASON_SYNC,
1396        };
1397
1398        /* Nothing to do? */
1399        if (sb->s_bdi == &noop_backing_dev_info)
1400                return;
1401        WARN_ON(!rwsem_is_locked(&sb->s_umount));
1402
1403        bdi_queue_work(sb->s_bdi, &work);
1404        wait_for_completion(&done);
1405
1406        wait_sb_inodes(sb);
1407}
1408EXPORT_SYMBOL(sync_inodes_sb);
1409
1410/**
1411 * write_inode_now      -       write an inode to disk
1412 * @inode: inode to write to disk
1413 * @sync: whether the write should be synchronous or not
1414 *
1415 * This function commits an inode to disk immediately if it is dirty. This is
1416 * primarily needed by knfsd.
1417 *
1418 * The caller must either have a ref on the inode or must have set I_WILL_FREE.
1419 */
1420int write_inode_now(struct inode *inode, int sync)
1421{
1422        struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
1423        struct writeback_control wbc = {
1424                .nr_to_write = LONG_MAX,
1425                .sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
1426                .range_start = 0,
1427                .range_end = LLONG_MAX,
1428        };
1429
1430        if (!mapping_cap_writeback_dirty(inode->i_mapping))
1431                wbc.nr_to_write = 0;
1432
1433        might_sleep();
1434        return writeback_single_inode(inode, wb, &wbc);
1435}
1436EXPORT_SYMBOL(write_inode_now);
1437
1438/**
1439 * sync_inode - write an inode and its pages to disk.
1440 * @inode: the inode to sync
1441 * @wbc: controls the writeback mode
1442 *
1443 * sync_inode() will write an inode and its pages to disk.  It will also
1444 * correctly update the inode on its superblock's dirty inode lists and will
1445 * update inode->i_state.
1446 *
1447 * The caller must have a ref on the inode.
1448 */
1449int sync_inode(struct inode *inode, struct writeback_control *wbc)
1450{
1451        return writeback_single_inode(inode, &inode_to_bdi(inode)->wb, wbc);
1452}
1453EXPORT_SYMBOL(sync_inode);
1454
1455/**
1456 * sync_inode_metadata - write an inode to disk
1457 * @inode: the inode to sync
1458 * @wait: wait for I/O to complete.
1459 *
1460 * Write an inode to disk and adjust its dirty state after completion.
1461 *
1462 * Note: only writes the actual inode, no associated data or other metadata.
1463 */
1464int sync_inode_metadata(struct inode *inode, int wait)
1465{
1466        struct writeback_control wbc = {
1467                .sync_mode = wait ? WB_SYNC_ALL : WB_SYNC_NONE,
1468                .nr_to_write = 0, /* metadata-only */
1469        };
1470
1471        return sync_inode(inode, &wbc);
1472}
1473EXPORT_SYMBOL(sync_inode_metadata);
1474
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