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