ASoC: Manage mode and rate bits correctly for CS4271 CODEC.
[pandora-kernel.git] / fs / fs-writeback.c
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/module.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/kthread.h>
24 #include <linux/freezer.h>
25 #include <linux/writeback.h>
26 #include <linux/blkdev.h>
27 #include <linux/backing-dev.h>
28 #include <linux/buffer_head.h>
29 #include <linux/tracepoint.h>
30 #include "internal.h"
31
32 /*
33  * Passed into wb_writeback(), essentially a subset of writeback_control
34  */
35 struct wb_writeback_work {
36         long nr_pages;
37         struct super_block *sb;
38         enum writeback_sync_modes sync_mode;
39         unsigned int for_kupdate:1;
40         unsigned int range_cyclic:1;
41         unsigned int for_background:1;
42
43         struct list_head list;          /* pending work list */
44         struct completion *done;        /* set if the caller waits */
45 };
46
47 /*
48  * Include the creation of the trace points after defining the
49  * wb_writeback_work structure so that the definition remains local to this
50  * file.
51  */
52 #define CREATE_TRACE_POINTS
53 #include <trace/events/writeback.h>
54
55 /*
56  * We don't actually have pdflush, but this one is exported though /proc...
57  */
58 int 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  */
67 int writeback_in_progress(struct backing_dev_info *bdi)
68 {
69         return test_bit(BDI_writeback_running, &bdi->state);
70 }
71
72 static 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
82 static inline struct inode *wb_inode(struct list_head *head)
83 {
84         return list_entry(head, struct inode, i_wb_list);
85 }
86
87 /* Wakeup flusher thread or forker thread to fork it. Requires bdi->wb_lock. */
88 static void bdi_wakeup_flusher(struct backing_dev_info *bdi)
89 {
90         if (bdi->wb.task) {
91                 wake_up_process(bdi->wb.task);
92         } else {
93                 /*
94                  * The bdi thread isn't there, wake up the forker thread which
95                  * will create and run it.
96                  */
97                 wake_up_process(default_backing_dev_info.wb.task);
98         }
99 }
100
101 static void bdi_queue_work(struct backing_dev_info *bdi,
102                            struct wb_writeback_work *work)
103 {
104         trace_writeback_queue(bdi, work);
105
106         spin_lock_bh(&bdi->wb_lock);
107         list_add_tail(&work->list, &bdi->work_list);
108         if (!bdi->wb.task)
109                 trace_writeback_nothread(bdi, work);
110         bdi_wakeup_flusher(bdi);
111         spin_unlock_bh(&bdi->wb_lock);
112 }
113
114 static void
115 __bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
116                       bool range_cyclic)
117 {
118         struct wb_writeback_work *work;
119
120         /*
121          * This is WB_SYNC_NONE writeback, so if allocation fails just
122          * wakeup the thread for old dirty data writeback
123          */
124         work = kzalloc(sizeof(*work), GFP_ATOMIC);
125         if (!work) {
126                 if (bdi->wb.task) {
127                         trace_writeback_nowork(bdi);
128                         wake_up_process(bdi->wb.task);
129                 }
130                 return;
131         }
132
133         work->sync_mode = WB_SYNC_NONE;
134         work->nr_pages  = nr_pages;
135         work->range_cyclic = range_cyclic;
136
137         bdi_queue_work(bdi, work);
138 }
139
140 /**
141  * bdi_start_writeback - start writeback
142  * @bdi: the backing device to write from
143  * @nr_pages: the number of pages to write
144  *
145  * Description:
146  *   This does WB_SYNC_NONE opportunistic writeback. The IO is only
147  *   started when this function returns, we make no guarentees on
148  *   completion. Caller need not hold sb s_umount semaphore.
149  *
150  */
151 void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages)
152 {
153         __bdi_start_writeback(bdi, nr_pages, true);
154 }
155
156 /**
157  * bdi_start_background_writeback - start background writeback
158  * @bdi: the backing device to write from
159  *
160  * Description:
161  *   This makes sure WB_SYNC_NONE background writeback happens. When
162  *   this function returns, it is only guaranteed that for given BDI
163  *   some IO is happening if we are over background dirty threshold.
164  *   Caller need not hold sb s_umount semaphore.
165  */
166 void bdi_start_background_writeback(struct backing_dev_info *bdi)
167 {
168         /*
169          * We just wake up the flusher thread. It will perform background
170          * writeback as soon as there is no other work to do.
171          */
172         trace_writeback_wake_background(bdi);
173         spin_lock_bh(&bdi->wb_lock);
174         bdi_wakeup_flusher(bdi);
175         spin_unlock_bh(&bdi->wb_lock);
176 }
177
178 /*
179  * Redirty an inode: set its when-it-was dirtied timestamp and move it to the
180  * furthest end of its superblock's dirty-inode list.
181  *
182  * Before stamping the inode's ->dirtied_when, we check to see whether it is
183  * already the most-recently-dirtied inode on the b_dirty list.  If that is
184  * the case then the inode must have been redirtied while it was being written
185  * out and we don't reset its dirtied_when.
186  */
187 static void redirty_tail(struct inode *inode)
188 {
189         struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
190
191         if (!list_empty(&wb->b_dirty)) {
192                 struct inode *tail;
193
194                 tail = wb_inode(wb->b_dirty.next);
195                 if (time_before(inode->dirtied_when, tail->dirtied_when))
196                         inode->dirtied_when = jiffies;
197         }
198         list_move(&inode->i_wb_list, &wb->b_dirty);
199 }
200
201 /*
202  * requeue inode for re-scanning after bdi->b_io list is exhausted.
203  */
204 static void requeue_io(struct inode *inode)
205 {
206         struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
207
208         list_move(&inode->i_wb_list, &wb->b_more_io);
209 }
210
211 static void inode_sync_complete(struct inode *inode)
212 {
213         /*
214          * Prevent speculative execution through spin_unlock(&inode_lock);
215          */
216         smp_mb();
217         wake_up_bit(&inode->i_state, __I_SYNC);
218 }
219
220 static bool inode_dirtied_after(struct inode *inode, unsigned long t)
221 {
222         bool ret = time_after(inode->dirtied_when, t);
223 #ifndef CONFIG_64BIT
224         /*
225          * For inodes being constantly redirtied, dirtied_when can get stuck.
226          * It _appears_ to be in the future, but is actually in distant past.
227          * This test is necessary to prevent such wrapped-around relative times
228          * from permanently stopping the whole bdi writeback.
229          */
230         ret = ret && time_before_eq(inode->dirtied_when, jiffies);
231 #endif
232         return ret;
233 }
234
235 /*
236  * Move expired dirty inodes from @delaying_queue to @dispatch_queue.
237  */
238 static void move_expired_inodes(struct list_head *delaying_queue,
239                                struct list_head *dispatch_queue,
240                                 unsigned long *older_than_this)
241 {
242         LIST_HEAD(tmp);
243         struct list_head *pos, *node;
244         struct super_block *sb = NULL;
245         struct inode *inode;
246         int do_sb_sort = 0;
247
248         while (!list_empty(delaying_queue)) {
249                 inode = wb_inode(delaying_queue->prev);
250                 if (older_than_this &&
251                     inode_dirtied_after(inode, *older_than_this))
252                         break;
253                 if (sb && sb != inode->i_sb)
254                         do_sb_sort = 1;
255                 sb = inode->i_sb;
256                 list_move(&inode->i_wb_list, &tmp);
257         }
258
259         /* just one sb in list, splice to dispatch_queue and we're done */
260         if (!do_sb_sort) {
261                 list_splice(&tmp, dispatch_queue);
262                 return;
263         }
264
265         /* Move inodes from one superblock together */
266         while (!list_empty(&tmp)) {
267                 sb = wb_inode(tmp.prev)->i_sb;
268                 list_for_each_prev_safe(pos, node, &tmp) {
269                         inode = wb_inode(pos);
270                         if (inode->i_sb == sb)
271                                 list_move(&inode->i_wb_list, dispatch_queue);
272                 }
273         }
274 }
275
276 /*
277  * Queue all expired dirty inodes for io, eldest first.
278  * Before
279  *         newly dirtied     b_dirty    b_io    b_more_io
280  *         =============>    gf         edc     BA
281  * After
282  *         newly dirtied     b_dirty    b_io    b_more_io
283  *         =============>    g          fBAedc
284  *                                           |
285  *                                           +--> dequeue for IO
286  */
287 static void queue_io(struct bdi_writeback *wb, unsigned long *older_than_this)
288 {
289         list_splice_init(&wb->b_more_io, &wb->b_io);
290         move_expired_inodes(&wb->b_dirty, &wb->b_io, older_than_this);
291 }
292
293 static int write_inode(struct inode *inode, struct writeback_control *wbc)
294 {
295         if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode))
296                 return inode->i_sb->s_op->write_inode(inode, wbc);
297         return 0;
298 }
299
300 /*
301  * Wait for writeback on an inode to complete.
302  */
303 static void inode_wait_for_writeback(struct inode *inode)
304 {
305         DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
306         wait_queue_head_t *wqh;
307
308         wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
309          while (inode->i_state & I_SYNC) {
310                 spin_unlock(&inode_lock);
311                 __wait_on_bit(wqh, &wq, inode_wait, TASK_UNINTERRUPTIBLE);
312                 spin_lock(&inode_lock);
313         }
314 }
315
316 /*
317  * Write out an inode's dirty pages.  Called under inode_lock.  Either the
318  * caller has ref on the inode (either via __iget or via syscall against an fd)
319  * or the inode has I_WILL_FREE set (via generic_forget_inode)
320  *
321  * If `wait' is set, wait on the writeout.
322  *
323  * The whole writeout design is quite complex and fragile.  We want to avoid
324  * starvation of particular inodes when others are being redirtied, prevent
325  * livelocks, etc.
326  *
327  * Called under inode_lock.
328  */
329 static int
330 writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
331 {
332         struct address_space *mapping = inode->i_mapping;
333         unsigned dirty;
334         int ret;
335
336         if (!atomic_read(&inode->i_count))
337                 WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
338         else
339                 WARN_ON(inode->i_state & I_WILL_FREE);
340
341         if (inode->i_state & I_SYNC) {
342                 /*
343                  * If this inode is locked for writeback and we are not doing
344                  * writeback-for-data-integrity, move it to b_more_io so that
345                  * writeback can proceed with the other inodes on s_io.
346                  *
347                  * We'll have another go at writing back this inode when we
348                  * completed a full scan of b_io.
349                  */
350                 if (wbc->sync_mode != WB_SYNC_ALL) {
351                         requeue_io(inode);
352                         return 0;
353                 }
354
355                 /*
356                  * It's a data-integrity sync.  We must wait.
357                  */
358                 inode_wait_for_writeback(inode);
359         }
360
361         BUG_ON(inode->i_state & I_SYNC);
362
363         /* Set I_SYNC, reset I_DIRTY_PAGES */
364         inode->i_state |= I_SYNC;
365         inode->i_state &= ~I_DIRTY_PAGES;
366         spin_unlock(&inode_lock);
367
368         ret = do_writepages(mapping, wbc);
369
370         /*
371          * Make sure to wait on the data before writing out the metadata.
372          * This is important for filesystems that modify metadata on data
373          * I/O completion.
374          */
375         if (wbc->sync_mode == WB_SYNC_ALL) {
376                 int err = filemap_fdatawait(mapping);
377                 if (ret == 0)
378                         ret = err;
379         }
380
381         /*
382          * Some filesystems may redirty the inode during the writeback
383          * due to delalloc, clear dirty metadata flags right before
384          * write_inode()
385          */
386         spin_lock(&inode_lock);
387         dirty = inode->i_state & I_DIRTY;
388         inode->i_state &= ~(I_DIRTY_SYNC | I_DIRTY_DATASYNC);
389         spin_unlock(&inode_lock);
390         /* Don't write the inode if only I_DIRTY_PAGES was set */
391         if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
392                 int err = write_inode(inode, wbc);
393                 if (ret == 0)
394                         ret = err;
395         }
396
397         spin_lock(&inode_lock);
398         inode->i_state &= ~I_SYNC;
399         if (!(inode->i_state & I_FREEING)) {
400                 if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
401                         /*
402                          * We didn't write back all the pages.  nfs_writepages()
403                          * sometimes bales out without doing anything.
404                          */
405                         inode->i_state |= I_DIRTY_PAGES;
406                         if (wbc->nr_to_write <= 0) {
407                                 /*
408                                  * slice used up: queue for next turn
409                                  */
410                                 requeue_io(inode);
411                         } else {
412                                 /*
413                                  * Writeback blocked by something other than
414                                  * congestion. Delay the inode for some time to
415                                  * avoid spinning on the CPU (100% iowait)
416                                  * retrying writeback of the dirty page/inode
417                                  * that cannot be performed immediately.
418                                  */
419                                 redirty_tail(inode);
420                         }
421                 } else if (inode->i_state & I_DIRTY) {
422                         /*
423                          * Filesystems can dirty the inode during writeback
424                          * operations, such as delayed allocation during
425                          * submission or metadata updates after data IO
426                          * completion.
427                          */
428                         redirty_tail(inode);
429                 } else {
430                         /*
431                          * The inode is clean.  At this point we either have
432                          * a reference to the inode or it's on it's way out.
433                          * No need to add it back to the LRU.
434                          */
435                         list_del_init(&inode->i_wb_list);
436                 }
437         }
438         inode_sync_complete(inode);
439         return ret;
440 }
441
442 /*
443  * For background writeback the caller does not have the sb pinned
444  * before calling writeback. So make sure that we do pin it, so it doesn't
445  * go away while we are writing inodes from it.
446  */
447 static bool pin_sb_for_writeback(struct super_block *sb)
448 {
449         spin_lock(&sb_lock);
450         if (list_empty(&sb->s_instances)) {
451                 spin_unlock(&sb_lock);
452                 return false;
453         }
454
455         sb->s_count++;
456         spin_unlock(&sb_lock);
457
458         if (down_read_trylock(&sb->s_umount)) {
459                 if (sb->s_root)
460                         return true;
461                 up_read(&sb->s_umount);
462         }
463
464         put_super(sb);
465         return false;
466 }
467
468 /*
469  * Write a portion of b_io inodes which belong to @sb.
470  *
471  * If @only_this_sb is true, then find and write all such
472  * inodes. Otherwise write only ones which go sequentially
473  * in reverse order.
474  *
475  * Return 1, if the caller writeback routine should be
476  * interrupted. Otherwise return 0.
477  */
478 static int writeback_sb_inodes(struct super_block *sb, struct bdi_writeback *wb,
479                 struct writeback_control *wbc, bool only_this_sb)
480 {
481         while (!list_empty(&wb->b_io)) {
482                 long pages_skipped;
483                 struct inode *inode = wb_inode(wb->b_io.prev);
484
485                 if (inode->i_sb != sb) {
486                         if (only_this_sb) {
487                                 /*
488                                  * We only want to write back data for this
489                                  * superblock, move all inodes not belonging
490                                  * to it back onto the dirty list.
491                                  */
492                                 redirty_tail(inode);
493                                 continue;
494                         }
495
496                         /*
497                          * The inode belongs to a different superblock.
498                          * Bounce back to the caller to unpin this and
499                          * pin the next superblock.
500                          */
501                         return 0;
502                 }
503
504                 /*
505                  * Don't bother with new inodes or inodes beeing freed, first
506                  * kind does not need peridic writeout yet, and for the latter
507                  * kind writeout is handled by the freer.
508                  */
509                 if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
510                         requeue_io(inode);
511                         continue;
512                 }
513
514                 /*
515                  * Was this inode dirtied after sync_sb_inodes was called?
516                  * This keeps sync from extra jobs and livelock.
517                  */
518                 if (inode_dirtied_after(inode, wbc->wb_start))
519                         return 1;
520
521                 __iget(inode);
522                 pages_skipped = wbc->pages_skipped;
523                 writeback_single_inode(inode, wbc);
524                 if (wbc->pages_skipped != pages_skipped) {
525                         /*
526                          * writeback is not making progress due to locked
527                          * buffers.  Skip this inode for now.
528                          */
529                         redirty_tail(inode);
530                 }
531                 spin_unlock(&inode_lock);
532                 iput(inode);
533                 cond_resched();
534                 spin_lock(&inode_lock);
535                 if (wbc->nr_to_write <= 0) {
536                         wbc->more_io = 1;
537                         return 1;
538                 }
539                 if (!list_empty(&wb->b_more_io))
540                         wbc->more_io = 1;
541         }
542         /* b_io is empty */
543         return 1;
544 }
545
546 void writeback_inodes_wb(struct bdi_writeback *wb,
547                 struct writeback_control *wbc)
548 {
549         int ret = 0;
550
551         if (!wbc->wb_start)
552                 wbc->wb_start = jiffies; /* livelock avoidance */
553         spin_lock(&inode_lock);
554         if (!wbc->for_kupdate || list_empty(&wb->b_io))
555                 queue_io(wb, wbc->older_than_this);
556
557         while (!list_empty(&wb->b_io)) {
558                 struct inode *inode = wb_inode(wb->b_io.prev);
559                 struct super_block *sb = inode->i_sb;
560
561                 if (!pin_sb_for_writeback(sb)) {
562                         requeue_io(inode);
563                         continue;
564                 }
565                 ret = writeback_sb_inodes(sb, wb, wbc, false);
566                 drop_super(sb);
567
568                 if (ret)
569                         break;
570         }
571         spin_unlock(&inode_lock);
572         /* Leave any unwritten inodes on b_io */
573 }
574
575 static void __writeback_inodes_sb(struct super_block *sb,
576                 struct bdi_writeback *wb, struct writeback_control *wbc)
577 {
578         WARN_ON(!rwsem_is_locked(&sb->s_umount));
579
580         spin_lock(&inode_lock);
581         if (!wbc->for_kupdate || list_empty(&wb->b_io))
582                 queue_io(wb, wbc->older_than_this);
583         writeback_sb_inodes(sb, wb, wbc, true);
584         spin_unlock(&inode_lock);
585 }
586
587 /*
588  * The maximum number of pages to writeout in a single bdi flush/kupdate
589  * operation.  We do this so we don't hold I_SYNC against an inode for
590  * enormous amounts of time, which would block a userspace task which has
591  * been forced to throttle against that inode.  Also, the code reevaluates
592  * the dirty each time it has written this many pages.
593  */
594 #define MAX_WRITEBACK_PAGES     1024
595
596 static inline bool over_bground_thresh(void)
597 {
598         unsigned long background_thresh, dirty_thresh;
599
600         global_dirty_limits(&background_thresh, &dirty_thresh);
601
602         return (global_page_state(NR_FILE_DIRTY) +
603                 global_page_state(NR_UNSTABLE_NFS) > background_thresh);
604 }
605
606 /*
607  * Explicit flushing or periodic writeback of "old" data.
608  *
609  * Define "old": the first time one of an inode's pages is dirtied, we mark the
610  * dirtying-time in the inode's address_space.  So this periodic writeback code
611  * just walks the superblock inode list, writing back any inodes which are
612  * older than a specific point in time.
613  *
614  * Try to run once per dirty_writeback_interval.  But if a writeback event
615  * takes longer than a dirty_writeback_interval interval, then leave a
616  * one-second gap.
617  *
618  * older_than_this takes precedence over nr_to_write.  So we'll only write back
619  * all dirty pages if they are all attached to "old" mappings.
620  */
621 static long wb_writeback(struct bdi_writeback *wb,
622                          struct wb_writeback_work *work)
623 {
624         struct writeback_control wbc = {
625                 .sync_mode              = work->sync_mode,
626                 .older_than_this        = NULL,
627                 .for_kupdate            = work->for_kupdate,
628                 .for_background         = work->for_background,
629                 .range_cyclic           = work->range_cyclic,
630         };
631         unsigned long oldest_jif;
632         long wrote = 0;
633         long write_chunk;
634         struct inode *inode;
635
636         if (wbc.for_kupdate) {
637                 wbc.older_than_this = &oldest_jif;
638                 oldest_jif = jiffies -
639                                 msecs_to_jiffies(dirty_expire_interval * 10);
640         }
641         if (!wbc.range_cyclic) {
642                 wbc.range_start = 0;
643                 wbc.range_end = LLONG_MAX;
644         }
645
646         /*
647          * WB_SYNC_ALL mode does livelock avoidance by syncing dirty
648          * inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
649          * here avoids calling into writeback_inodes_wb() more than once.
650          *
651          * The intended call sequence for WB_SYNC_ALL writeback is:
652          *
653          *      wb_writeback()
654          *          __writeback_inodes_sb()     <== called only once
655          *              write_cache_pages()     <== called once for each inode
656          *                   (quickly) tag currently dirty pages
657          *                   (maybe slowly) sync all tagged pages
658          */
659         if (wbc.sync_mode == WB_SYNC_NONE)
660                 write_chunk = MAX_WRITEBACK_PAGES;
661         else
662                 write_chunk = LONG_MAX;
663
664         wbc.wb_start = jiffies; /* livelock avoidance */
665         for (;;) {
666                 /*
667                  * Stop writeback when nr_pages has been consumed
668                  */
669                 if (work->nr_pages <= 0)
670                         break;
671
672                 /*
673                  * Background writeout and kupdate-style writeback may
674                  * run forever. Stop them if there is other work to do
675                  * so that e.g. sync can proceed. They'll be restarted
676                  * after the other works are all done.
677                  */
678                 if ((work->for_background || work->for_kupdate) &&
679                     !list_empty(&wb->bdi->work_list))
680                         break;
681
682                 /*
683                  * For background writeout, stop when we are below the
684                  * background dirty threshold
685                  */
686                 if (work->for_background && !over_bground_thresh())
687                         break;
688
689                 wbc.more_io = 0;
690                 wbc.nr_to_write = write_chunk;
691                 wbc.pages_skipped = 0;
692
693                 trace_wbc_writeback_start(&wbc, wb->bdi);
694                 if (work->sb)
695                         __writeback_inodes_sb(work->sb, wb, &wbc);
696                 else
697                         writeback_inodes_wb(wb, &wbc);
698                 trace_wbc_writeback_written(&wbc, wb->bdi);
699
700                 work->nr_pages -= write_chunk - wbc.nr_to_write;
701                 wrote += write_chunk - wbc.nr_to_write;
702
703                 /*
704                  * If we consumed everything, see if we have more
705                  */
706                 if (wbc.nr_to_write <= 0)
707                         continue;
708                 /*
709                  * Didn't write everything and we don't have more IO, bail
710                  */
711                 if (!wbc.more_io)
712                         break;
713                 /*
714                  * Did we write something? Try for more
715                  */
716                 if (wbc.nr_to_write < write_chunk)
717                         continue;
718                 /*
719                  * Nothing written. Wait for some inode to
720                  * become available for writeback. Otherwise
721                  * we'll just busyloop.
722                  */
723                 spin_lock(&inode_lock);
724                 if (!list_empty(&wb->b_more_io))  {
725                         inode = wb_inode(wb->b_more_io.prev);
726                         trace_wbc_writeback_wait(&wbc, wb->bdi);
727                         inode_wait_for_writeback(inode);
728                 }
729                 spin_unlock(&inode_lock);
730         }
731
732         return wrote;
733 }
734
735 /*
736  * Return the next wb_writeback_work struct that hasn't been processed yet.
737  */
738 static struct wb_writeback_work *
739 get_next_work_item(struct backing_dev_info *bdi)
740 {
741         struct wb_writeback_work *work = NULL;
742
743         spin_lock_bh(&bdi->wb_lock);
744         if (!list_empty(&bdi->work_list)) {
745                 work = list_entry(bdi->work_list.next,
746                                   struct wb_writeback_work, list);
747                 list_del_init(&work->list);
748         }
749         spin_unlock_bh(&bdi->wb_lock);
750         return work;
751 }
752
753 /*
754  * Add in the number of potentially dirty inodes, because each inode
755  * write can dirty pagecache in the underlying blockdev.
756  */
757 static unsigned long get_nr_dirty_pages(void)
758 {
759         return global_page_state(NR_FILE_DIRTY) +
760                 global_page_state(NR_UNSTABLE_NFS) +
761                 get_nr_dirty_inodes();
762 }
763
764 static long wb_check_background_flush(struct bdi_writeback *wb)
765 {
766         if (over_bground_thresh()) {
767
768                 struct wb_writeback_work work = {
769                         .nr_pages       = LONG_MAX,
770                         .sync_mode      = WB_SYNC_NONE,
771                         .for_background = 1,
772                         .range_cyclic   = 1,
773                 };
774
775                 return wb_writeback(wb, &work);
776         }
777
778         return 0;
779 }
780
781 static long wb_check_old_data_flush(struct bdi_writeback *wb)
782 {
783         unsigned long expired;
784         long nr_pages;
785
786         /*
787          * When set to zero, disable periodic writeback
788          */
789         if (!dirty_writeback_interval)
790                 return 0;
791
792         expired = wb->last_old_flush +
793                         msecs_to_jiffies(dirty_writeback_interval * 10);
794         if (time_before(jiffies, expired))
795                 return 0;
796
797         wb->last_old_flush = jiffies;
798         nr_pages = get_nr_dirty_pages();
799
800         if (nr_pages) {
801                 struct wb_writeback_work work = {
802                         .nr_pages       = nr_pages,
803                         .sync_mode      = WB_SYNC_NONE,
804                         .for_kupdate    = 1,
805                         .range_cyclic   = 1,
806                 };
807
808                 return wb_writeback(wb, &work);
809         }
810
811         return 0;
812 }
813
814 /*
815  * Retrieve work items and do the writeback they describe
816  */
817 long wb_do_writeback(struct bdi_writeback *wb, int force_wait)
818 {
819         struct backing_dev_info *bdi = wb->bdi;
820         struct wb_writeback_work *work;
821         long wrote = 0;
822
823         set_bit(BDI_writeback_running, &wb->bdi->state);
824         while ((work = get_next_work_item(bdi)) != NULL) {
825                 /*
826                  * Override sync mode, in case we must wait for completion
827                  * because this thread is exiting now.
828                  */
829                 if (force_wait)
830                         work->sync_mode = WB_SYNC_ALL;
831
832                 trace_writeback_exec(bdi, work);
833
834                 wrote += wb_writeback(wb, work);
835
836                 /*
837                  * Notify the caller of completion if this is a synchronous
838                  * work item, otherwise just free it.
839                  */
840                 if (work->done)
841                         complete(work->done);
842                 else
843                         kfree(work);
844         }
845
846         /*
847          * Check for periodic writeback, kupdated() style
848          */
849         wrote += wb_check_old_data_flush(wb);
850         wrote += wb_check_background_flush(wb);
851         clear_bit(BDI_writeback_running, &wb->bdi->state);
852
853         return wrote;
854 }
855
856 /*
857  * Handle writeback of dirty data for the device backed by this bdi. Also
858  * wakes up periodically and does kupdated style flushing.
859  */
860 int bdi_writeback_thread(void *data)
861 {
862         struct bdi_writeback *wb = data;
863         struct backing_dev_info *bdi = wb->bdi;
864         long pages_written;
865
866         current->flags |= PF_SWAPWRITE;
867         set_freezable();
868         wb->last_active = jiffies;
869
870         /*
871          * Our parent may run at a different priority, just set us to normal
872          */
873         set_user_nice(current, 0);
874
875         trace_writeback_thread_start(bdi);
876
877         while (!kthread_should_stop()) {
878                 /*
879                  * Remove own delayed wake-up timer, since we are already awake
880                  * and we'll take care of the preriodic write-back.
881                  */
882                 del_timer(&wb->wakeup_timer);
883
884                 pages_written = wb_do_writeback(wb, 0);
885
886                 trace_writeback_pages_written(pages_written);
887
888                 if (pages_written)
889                         wb->last_active = jiffies;
890
891                 set_current_state(TASK_INTERRUPTIBLE);
892                 if (!list_empty(&bdi->work_list) || kthread_should_stop()) {
893                         __set_current_state(TASK_RUNNING);
894                         continue;
895                 }
896
897                 if (wb_has_dirty_io(wb) && dirty_writeback_interval)
898                         schedule_timeout(msecs_to_jiffies(dirty_writeback_interval * 10));
899                 else {
900                         /*
901                          * We have nothing to do, so can go sleep without any
902                          * timeout and save power. When a work is queued or
903                          * something is made dirty - we will be woken up.
904                          */
905                         schedule();
906                 }
907
908                 try_to_freeze();
909         }
910
911         /* Flush any work that raced with us exiting */
912         if (!list_empty(&bdi->work_list))
913                 wb_do_writeback(wb, 1);
914
915         trace_writeback_thread_stop(bdi);
916         return 0;
917 }
918
919
920 /*
921  * Start writeback of `nr_pages' pages.  If `nr_pages' is zero, write back
922  * the whole world.
923  */
924 void wakeup_flusher_threads(long nr_pages)
925 {
926         struct backing_dev_info *bdi;
927
928         if (!nr_pages) {
929                 nr_pages = global_page_state(NR_FILE_DIRTY) +
930                                 global_page_state(NR_UNSTABLE_NFS);
931         }
932
933         rcu_read_lock();
934         list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
935                 if (!bdi_has_dirty_io(bdi))
936                         continue;
937                 __bdi_start_writeback(bdi, nr_pages, false);
938         }
939         rcu_read_unlock();
940 }
941
942 static noinline void block_dump___mark_inode_dirty(struct inode *inode)
943 {
944         if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) {
945                 struct dentry *dentry;
946                 const char *name = "?";
947
948                 dentry = d_find_alias(inode);
949                 if (dentry) {
950                         spin_lock(&dentry->d_lock);
951                         name = (const char *) dentry->d_name.name;
952                 }
953                 printk(KERN_DEBUG
954                        "%s(%d): dirtied inode %lu (%s) on %s\n",
955                        current->comm, task_pid_nr(current), inode->i_ino,
956                        name, inode->i_sb->s_id);
957                 if (dentry) {
958                         spin_unlock(&dentry->d_lock);
959                         dput(dentry);
960                 }
961         }
962 }
963
964 /**
965  *      __mark_inode_dirty -    internal function
966  *      @inode: inode to mark
967  *      @flags: what kind of dirty (i.e. I_DIRTY_SYNC)
968  *      Mark an inode as dirty. Callers should use mark_inode_dirty or
969  *      mark_inode_dirty_sync.
970  *
971  * Put the inode on the super block's dirty list.
972  *
973  * CAREFUL! We mark it dirty unconditionally, but move it onto the
974  * dirty list only if it is hashed or if it refers to a blockdev.
975  * If it was not hashed, it will never be added to the dirty list
976  * even if it is later hashed, as it will have been marked dirty already.
977  *
978  * In short, make sure you hash any inodes _before_ you start marking
979  * them dirty.
980  *
981  * This function *must* be atomic for the I_DIRTY_PAGES case -
982  * set_page_dirty() is called under spinlock in several places.
983  *
984  * Note that for blockdevs, inode->dirtied_when represents the dirtying time of
985  * the block-special inode (/dev/hda1) itself.  And the ->dirtied_when field of
986  * the kernel-internal blockdev inode represents the dirtying time of the
987  * blockdev's pages.  This is why for I_DIRTY_PAGES we always use
988  * page->mapping->host, so the page-dirtying time is recorded in the internal
989  * blockdev inode.
990  */
991 void __mark_inode_dirty(struct inode *inode, int flags)
992 {
993         struct super_block *sb = inode->i_sb;
994         struct backing_dev_info *bdi = NULL;
995         bool wakeup_bdi = false;
996
997         /*
998          * Don't do this for I_DIRTY_PAGES - that doesn't actually
999          * dirty the inode itself
1000          */
1001         if (flags & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
1002                 if (sb->s_op->dirty_inode)
1003                         sb->s_op->dirty_inode(inode);
1004         }
1005
1006         /*
1007          * make sure that changes are seen by all cpus before we test i_state
1008          * -- mikulas
1009          */
1010         smp_mb();
1011
1012         /* avoid the locking if we can */
1013         if ((inode->i_state & flags) == flags)
1014                 return;
1015
1016         if (unlikely(block_dump))
1017                 block_dump___mark_inode_dirty(inode);
1018
1019         spin_lock(&inode_lock);
1020         if ((inode->i_state & flags) != flags) {
1021                 const int was_dirty = inode->i_state & I_DIRTY;
1022
1023                 inode->i_state |= flags;
1024
1025                 /*
1026                  * If the inode is being synced, just update its dirty state.
1027                  * The unlocker will place the inode on the appropriate
1028                  * superblock list, based upon its state.
1029                  */
1030                 if (inode->i_state & I_SYNC)
1031                         goto out;
1032
1033                 /*
1034                  * Only add valid (hashed) inodes to the superblock's
1035                  * dirty list.  Add blockdev inodes as well.
1036                  */
1037                 if (!S_ISBLK(inode->i_mode)) {
1038                         if (inode_unhashed(inode))
1039                                 goto out;
1040                 }
1041                 if (inode->i_state & I_FREEING)
1042                         goto out;
1043
1044                 /*
1045                  * If the inode was already on b_dirty/b_io/b_more_io, don't
1046                  * reposition it (that would break b_dirty time-ordering).
1047                  */
1048                 if (!was_dirty) {
1049                         bdi = inode_to_bdi(inode);
1050
1051                         if (bdi_cap_writeback_dirty(bdi)) {
1052                                 WARN(!test_bit(BDI_registered, &bdi->state),
1053                                      "bdi-%s not registered\n", bdi->name);
1054
1055                                 /*
1056                                  * If this is the first dirty inode for this
1057                                  * bdi, we have to wake-up the corresponding
1058                                  * bdi thread to make sure background
1059                                  * write-back happens later.
1060                                  */
1061                                 if (!wb_has_dirty_io(&bdi->wb))
1062                                         wakeup_bdi = true;
1063                         }
1064
1065                         inode->dirtied_when = jiffies;
1066                         list_move(&inode->i_wb_list, &bdi->wb.b_dirty);
1067                 }
1068         }
1069 out:
1070         spin_unlock(&inode_lock);
1071
1072         if (wakeup_bdi)
1073                 bdi_wakeup_thread_delayed(bdi);
1074 }
1075 EXPORT_SYMBOL(__mark_inode_dirty);
1076
1077 /*
1078  * Write out a superblock's list of dirty inodes.  A wait will be performed
1079  * upon no inodes, all inodes or the final one, depending upon sync_mode.
1080  *
1081  * If older_than_this is non-NULL, then only write out inodes which
1082  * had their first dirtying at a time earlier than *older_than_this.
1083  *
1084  * If `bdi' is non-zero then we're being asked to writeback a specific queue.
1085  * This function assumes that the blockdev superblock's inodes are backed by
1086  * a variety of queues, so all inodes are searched.  For other superblocks,
1087  * assume that all inodes are backed by the same queue.
1088  *
1089  * The inodes to be written are parked on bdi->b_io.  They are moved back onto
1090  * bdi->b_dirty as they are selected for writing.  This way, none can be missed
1091  * on the writer throttling path, and we get decent balancing between many
1092  * throttled threads: we don't want them all piling up on inode_sync_wait.
1093  */
1094 static void wait_sb_inodes(struct super_block *sb)
1095 {
1096         struct inode *inode, *old_inode = NULL;
1097
1098         /*
1099          * We need to be protected against the filesystem going from
1100          * r/o to r/w or vice versa.
1101          */
1102         WARN_ON(!rwsem_is_locked(&sb->s_umount));
1103
1104         spin_lock(&inode_lock);
1105
1106         /*
1107          * Data integrity sync. Must wait for all pages under writeback,
1108          * because there may have been pages dirtied before our sync
1109          * call, but which had writeout started before we write it out.
1110          * In which case, the inode may not be on the dirty list, but
1111          * we still have to wait for that writeout.
1112          */
1113         list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
1114                 struct address_space *mapping;
1115
1116                 if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW))
1117                         continue;
1118                 mapping = inode->i_mapping;
1119                 if (mapping->nrpages == 0)
1120                         continue;
1121                 __iget(inode);
1122                 spin_unlock(&inode_lock);
1123                 /*
1124                  * We hold a reference to 'inode' so it couldn't have
1125                  * been removed from s_inodes list while we dropped the
1126                  * inode_lock.  We cannot iput the inode now as we can
1127                  * be holding the last reference and we cannot iput it
1128                  * under inode_lock. So we keep the reference and iput
1129                  * it later.
1130                  */
1131                 iput(old_inode);
1132                 old_inode = inode;
1133
1134                 filemap_fdatawait(mapping);
1135
1136                 cond_resched();
1137
1138                 spin_lock(&inode_lock);
1139         }
1140         spin_unlock(&inode_lock);
1141         iput(old_inode);
1142 }
1143
1144 /**
1145  * writeback_inodes_sb_nr -     writeback dirty inodes from given super_block
1146  * @sb: the superblock
1147  * @nr: the number of pages to write
1148  *
1149  * Start writeback on some inodes on this super_block. No guarantees are made
1150  * on how many (if any) will be written, and this function does not wait
1151  * for IO completion of submitted IO.
1152  */
1153 void writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr)
1154 {
1155         DECLARE_COMPLETION_ONSTACK(done);
1156         struct wb_writeback_work work = {
1157                 .sb             = sb,
1158                 .sync_mode      = WB_SYNC_NONE,
1159                 .done           = &done,
1160                 .nr_pages       = nr,
1161         };
1162
1163         WARN_ON(!rwsem_is_locked(&sb->s_umount));
1164         bdi_queue_work(sb->s_bdi, &work);
1165         wait_for_completion(&done);
1166 }
1167 EXPORT_SYMBOL(writeback_inodes_sb_nr);
1168
1169 /**
1170  * writeback_inodes_sb  -       writeback dirty inodes from given super_block
1171  * @sb: the superblock
1172  *
1173  * Start writeback on some inodes on this super_block. No guarantees are made
1174  * on how many (if any) will be written, and this function does not wait
1175  * for IO completion of submitted IO.
1176  */
1177 void writeback_inodes_sb(struct super_block *sb)
1178 {
1179         return writeback_inodes_sb_nr(sb, get_nr_dirty_pages());
1180 }
1181 EXPORT_SYMBOL(writeback_inodes_sb);
1182
1183 /**
1184  * writeback_inodes_sb_if_idle  -       start writeback if none underway
1185  * @sb: the superblock
1186  *
1187  * Invoke writeback_inodes_sb if no writeback is currently underway.
1188  * Returns 1 if writeback was started, 0 if not.
1189  */
1190 int writeback_inodes_sb_if_idle(struct super_block *sb)
1191 {
1192         if (!writeback_in_progress(sb->s_bdi)) {
1193                 down_read(&sb->s_umount);
1194                 writeback_inodes_sb(sb);
1195                 up_read(&sb->s_umount);
1196                 return 1;
1197         } else
1198                 return 0;
1199 }
1200 EXPORT_SYMBOL(writeback_inodes_sb_if_idle);
1201
1202 /**
1203  * writeback_inodes_sb_if_idle  -       start writeback if none underway
1204  * @sb: the superblock
1205  * @nr: the number of pages to write
1206  *
1207  * Invoke writeback_inodes_sb if no writeback is currently underway.
1208  * Returns 1 if writeback was started, 0 if not.
1209  */
1210 int writeback_inodes_sb_nr_if_idle(struct super_block *sb,
1211                                    unsigned long nr)
1212 {
1213         if (!writeback_in_progress(sb->s_bdi)) {
1214                 down_read(&sb->s_umount);
1215                 writeback_inodes_sb_nr(sb, nr);
1216                 up_read(&sb->s_umount);
1217                 return 1;
1218         } else
1219                 return 0;
1220 }
1221 EXPORT_SYMBOL(writeback_inodes_sb_nr_if_idle);
1222
1223 /**
1224  * sync_inodes_sb       -       sync sb inode pages
1225  * @sb: the superblock
1226  *
1227  * This function writes and waits on any dirty inode belonging to this
1228  * super_block.
1229  */
1230 void sync_inodes_sb(struct super_block *sb)
1231 {
1232         DECLARE_COMPLETION_ONSTACK(done);
1233         struct wb_writeback_work work = {
1234                 .sb             = sb,
1235                 .sync_mode      = WB_SYNC_ALL,
1236                 .nr_pages       = LONG_MAX,
1237                 .range_cyclic   = 0,
1238                 .done           = &done,
1239         };
1240
1241         WARN_ON(!rwsem_is_locked(&sb->s_umount));
1242
1243         bdi_queue_work(sb->s_bdi, &work);
1244         wait_for_completion(&done);
1245
1246         wait_sb_inodes(sb);
1247 }
1248 EXPORT_SYMBOL(sync_inodes_sb);
1249
1250 /**
1251  * write_inode_now      -       write an inode to disk
1252  * @inode: inode to write to disk
1253  * @sync: whether the write should be synchronous or not
1254  *
1255  * This function commits an inode to disk immediately if it is dirty. This is
1256  * primarily needed by knfsd.
1257  *
1258  * The caller must either have a ref on the inode or must have set I_WILL_FREE.
1259  */
1260 int write_inode_now(struct inode *inode, int sync)
1261 {
1262         int ret;
1263         struct writeback_control wbc = {
1264                 .nr_to_write = LONG_MAX,
1265                 .sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
1266                 .range_start = 0,
1267                 .range_end = LLONG_MAX,
1268         };
1269
1270         if (!mapping_cap_writeback_dirty(inode->i_mapping))
1271                 wbc.nr_to_write = 0;
1272
1273         might_sleep();
1274         spin_lock(&inode_lock);
1275         ret = writeback_single_inode(inode, &wbc);
1276         spin_unlock(&inode_lock);
1277         if (sync)
1278                 inode_sync_wait(inode);
1279         return ret;
1280 }
1281 EXPORT_SYMBOL(write_inode_now);
1282
1283 /**
1284  * sync_inode - write an inode and its pages to disk.
1285  * @inode: the inode to sync
1286  * @wbc: controls the writeback mode
1287  *
1288  * sync_inode() will write an inode and its pages to disk.  It will also
1289  * correctly update the inode on its superblock's dirty inode lists and will
1290  * update inode->i_state.
1291  *
1292  * The caller must have a ref on the inode.
1293  */
1294 int sync_inode(struct inode *inode, struct writeback_control *wbc)
1295 {
1296         int ret;
1297
1298         spin_lock(&inode_lock);
1299         ret = writeback_single_inode(inode, wbc);
1300         spin_unlock(&inode_lock);
1301         return ret;
1302 }
1303 EXPORT_SYMBOL(sync_inode);
1304
1305 /**
1306  * sync_inode_metadata - write an inode to disk
1307  * @inode: the inode to sync
1308  * @wait: wait for I/O to complete.
1309  *
1310  * Write an inode to disk and adjust its dirty state after completion.
1311  *
1312  * Note: only writes the actual inode, no associated data or other metadata.
1313  */
1314 int sync_inode_metadata(struct inode *inode, int wait)
1315 {
1316         struct writeback_control wbc = {
1317                 .sync_mode = wait ? WB_SYNC_ALL : WB_SYNC_NONE,
1318                 .nr_to_write = 0, /* metadata-only */
1319         };
1320
1321         return sync_inode(inode, &wbc);
1322 }
1323 EXPORT_SYMBOL(sync_inode_metadata);