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