linux/fs/fs-writeback.c
Tejun Heo 9c6ac78eb3 writeback: fix a subtle race condition in I_DIRTY clearing
After invoking ->dirty_inode(), __mark_inode_dirty() does smp_mb() and
tests inode->i_state locklessly to see whether it already has all the
necessary I_DIRTY bits set.  The comment above the barrier doesn't
contain any useful information - memory barriers can't ensure "changes
are seen by all cpus" by itself.

And it sure enough was broken.  Please consider the following
scenario.

 CPU 0					CPU 1
 -------------------------------------------------------------------------------

					enters __writeback_single_inode()
					grabs inode->i_lock
					tests PAGECACHE_TAG_DIRTY which is clear
 enters __set_page_dirty()
 grabs mapping->tree_lock
 sets PAGECACHE_TAG_DIRTY
 releases mapping->tree_lock
 leaves __set_page_dirty()

 enters __mark_inode_dirty()
 smp_mb()
 sees I_DIRTY_PAGES set
 leaves __mark_inode_dirty()
					clears I_DIRTY_PAGES
					releases inode->i_lock

Now @inode has dirty pages w/ I_DIRTY_PAGES clear.  This doesn't seem
to lead to an immediately critical problem because requeue_inode()
later checks PAGECACHE_TAG_DIRTY instead of I_DIRTY_PAGES when
deciding whether the inode needs to be requeued for IO and there are
enough unintentional memory barriers inbetween, so while the inode
ends up with inconsistent I_DIRTY_PAGES flag, it doesn't fall off the
IO list.

The lack of explicit barrier may also theoretically affect the other
I_DIRTY bits which deal with metadata dirtiness.  There is no
guarantee that a strong enough barrier exists between
I_DIRTY_[DATA]SYNC clearing and write_inode() writing out the dirtied
inode.  Filesystem inode writeout path likely has enough stuff which
can behave as full barrier but it's theoretically possible that the
writeout may not see all the updates from ->dirty_inode().

Fix it by adding an explicit smp_mb() after I_DIRTY clearing.  Note
that I_DIRTY_PAGES needs a special treatment as it always needs to be
cleared to be interlocked with the lockless test on
__mark_inode_dirty() side.  It's cleared unconditionally and
reinstated after smp_mb() if the mapping still has dirty pages.

Also add comments explaining how and why the barriers are paired.

Lightly tested.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: stable@vger.kernel.org
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>
2014-11-04 10:42:23 -07:00

1477 lines
40 KiB
C

/*
* fs/fs-writeback.c
*
* Copyright (C) 2002, Linus Torvalds.
*
* Contains all the functions related to writing back and waiting
* upon dirty inodes against superblocks, and writing back dirty
* pages against inodes. ie: data writeback. Writeout of the
* inode itself is not handled here.
*
* 10Apr2002 Andrew Morton
* Split out of fs/inode.c
* Additions for address_space-based writeback
*/
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/spinlock.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/kthread.h>
#include <linux/writeback.h>
#include <linux/blkdev.h>
#include <linux/backing-dev.h>
#include <linux/tracepoint.h>
#include <linux/device.h>
#include "internal.h"
/*
* 4MB minimal write chunk size
*/
#define MIN_WRITEBACK_PAGES (4096UL >> (PAGE_CACHE_SHIFT - 10))
/*
* Passed into wb_writeback(), essentially a subset of writeback_control
*/
struct wb_writeback_work {
long nr_pages;
struct super_block *sb;
unsigned long *older_than_this;
enum writeback_sync_modes sync_mode;
unsigned int tagged_writepages:1;
unsigned int for_kupdate:1;
unsigned int range_cyclic:1;
unsigned int for_background:1;
unsigned int for_sync:1; /* sync(2) WB_SYNC_ALL writeback */
enum wb_reason reason; /* why was writeback initiated? */
struct list_head list; /* pending work list */
struct completion *done; /* set if the caller waits */
};
/**
* writeback_in_progress - determine whether there is writeback in progress
* @bdi: the device's backing_dev_info structure.
*
* Determine whether there is writeback waiting to be handled against a
* backing device.
*/
int writeback_in_progress(struct backing_dev_info *bdi)
{
return test_bit(BDI_writeback_running, &bdi->state);
}
EXPORT_SYMBOL(writeback_in_progress);
static inline struct backing_dev_info *inode_to_bdi(struct inode *inode)
{
struct super_block *sb = inode->i_sb;
if (sb_is_blkdev_sb(sb))
return inode->i_mapping->backing_dev_info;
return sb->s_bdi;
}
static inline struct inode *wb_inode(struct list_head *head)
{
return list_entry(head, struct inode, i_wb_list);
}
/*
* Include the creation of the trace points after defining the
* wb_writeback_work structure and inline functions so that the definition
* remains local to this file.
*/
#define CREATE_TRACE_POINTS
#include <trace/events/writeback.h>
EXPORT_TRACEPOINT_SYMBOL_GPL(wbc_writepage);
static void bdi_wakeup_thread(struct backing_dev_info *bdi)
{
spin_lock_bh(&bdi->wb_lock);
if (test_bit(BDI_registered, &bdi->state))
mod_delayed_work(bdi_wq, &bdi->wb.dwork, 0);
spin_unlock_bh(&bdi->wb_lock);
}
static void bdi_queue_work(struct backing_dev_info *bdi,
struct wb_writeback_work *work)
{
trace_writeback_queue(bdi, work);
spin_lock_bh(&bdi->wb_lock);
if (!test_bit(BDI_registered, &bdi->state)) {
if (work->done)
complete(work->done);
goto out_unlock;
}
list_add_tail(&work->list, &bdi->work_list);
mod_delayed_work(bdi_wq, &bdi->wb.dwork, 0);
out_unlock:
spin_unlock_bh(&bdi->wb_lock);
}
static void
__bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
bool range_cyclic, enum wb_reason reason)
{
struct wb_writeback_work *work;
/*
* This is WB_SYNC_NONE writeback, so if allocation fails just
* wakeup the thread for old dirty data writeback
*/
work = kzalloc(sizeof(*work), GFP_ATOMIC);
if (!work) {
trace_writeback_nowork(bdi);
bdi_wakeup_thread(bdi);
return;
}
work->sync_mode = WB_SYNC_NONE;
work->nr_pages = nr_pages;
work->range_cyclic = range_cyclic;
work->reason = reason;
bdi_queue_work(bdi, work);
}
/**
* bdi_start_writeback - start writeback
* @bdi: the backing device to write from
* @nr_pages: the number of pages to write
* @reason: reason why some writeback work was initiated
*
* Description:
* This does WB_SYNC_NONE opportunistic writeback. The IO is only
* started when this function returns, we make no guarantees on
* completion. Caller need not hold sb s_umount semaphore.
*
*/
void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
enum wb_reason reason)
{
__bdi_start_writeback(bdi, nr_pages, true, reason);
}
/**
* bdi_start_background_writeback - start background writeback
* @bdi: the backing device to write from
*
* Description:
* This makes sure WB_SYNC_NONE background writeback happens. When
* this function returns, it is only guaranteed that for given BDI
* some IO is happening if we are over background dirty threshold.
* Caller need not hold sb s_umount semaphore.
*/
void bdi_start_background_writeback(struct backing_dev_info *bdi)
{
/*
* We just wake up the flusher thread. It will perform background
* writeback as soon as there is no other work to do.
*/
trace_writeback_wake_background(bdi);
bdi_wakeup_thread(bdi);
}
/*
* Remove the inode from the writeback list it is on.
*/
void inode_wb_list_del(struct inode *inode)
{
struct backing_dev_info *bdi = inode_to_bdi(inode);
spin_lock(&bdi->wb.list_lock);
list_del_init(&inode->i_wb_list);
spin_unlock(&bdi->wb.list_lock);
}
/*
* Redirty an inode: set its when-it-was dirtied timestamp and move it to the
* furthest end of its superblock's dirty-inode list.
*
* Before stamping the inode's ->dirtied_when, we check to see whether it is
* already the most-recently-dirtied inode on the b_dirty list. If that is
* the case then the inode must have been redirtied while it was being written
* out and we don't reset its dirtied_when.
*/
static void redirty_tail(struct inode *inode, struct bdi_writeback *wb)
{
assert_spin_locked(&wb->list_lock);
if (!list_empty(&wb->b_dirty)) {
struct inode *tail;
tail = wb_inode(wb->b_dirty.next);
if (time_before(inode->dirtied_when, tail->dirtied_when))
inode->dirtied_when = jiffies;
}
list_move(&inode->i_wb_list, &wb->b_dirty);
}
/*
* requeue inode for re-scanning after bdi->b_io list is exhausted.
*/
static void requeue_io(struct inode *inode, struct bdi_writeback *wb)
{
assert_spin_locked(&wb->list_lock);
list_move(&inode->i_wb_list, &wb->b_more_io);
}
static void inode_sync_complete(struct inode *inode)
{
inode->i_state &= ~I_SYNC;
/* If inode is clean an unused, put it into LRU now... */
inode_add_lru(inode);
/* Waiters must see I_SYNC cleared before being woken up */
smp_mb();
wake_up_bit(&inode->i_state, __I_SYNC);
}
static bool inode_dirtied_after(struct inode *inode, unsigned long t)
{
bool ret = time_after(inode->dirtied_when, t);
#ifndef CONFIG_64BIT
/*
* For inodes being constantly redirtied, dirtied_when can get stuck.
* It _appears_ to be in the future, but is actually in distant past.
* This test is necessary to prevent such wrapped-around relative times
* from permanently stopping the whole bdi writeback.
*/
ret = ret && time_before_eq(inode->dirtied_when, jiffies);
#endif
return ret;
}
/*
* Move expired (dirtied before work->older_than_this) dirty inodes from
* @delaying_queue to @dispatch_queue.
*/
static int move_expired_inodes(struct list_head *delaying_queue,
struct list_head *dispatch_queue,
struct wb_writeback_work *work)
{
LIST_HEAD(tmp);
struct list_head *pos, *node;
struct super_block *sb = NULL;
struct inode *inode;
int do_sb_sort = 0;
int moved = 0;
while (!list_empty(delaying_queue)) {
inode = wb_inode(delaying_queue->prev);
if (work->older_than_this &&
inode_dirtied_after(inode, *work->older_than_this))
break;
list_move(&inode->i_wb_list, &tmp);
moved++;
if (sb_is_blkdev_sb(inode->i_sb))
continue;
if (sb && sb != inode->i_sb)
do_sb_sort = 1;
sb = inode->i_sb;
}
/* just one sb in list, splice to dispatch_queue and we're done */
if (!do_sb_sort) {
list_splice(&tmp, dispatch_queue);
goto out;
}
/* Move inodes from one superblock together */
while (!list_empty(&tmp)) {
sb = wb_inode(tmp.prev)->i_sb;
list_for_each_prev_safe(pos, node, &tmp) {
inode = wb_inode(pos);
if (inode->i_sb == sb)
list_move(&inode->i_wb_list, dispatch_queue);
}
}
out:
return moved;
}
/*
* Queue all expired dirty inodes for io, eldest first.
* Before
* newly dirtied b_dirty b_io b_more_io
* =============> gf edc BA
* After
* newly dirtied b_dirty b_io b_more_io
* =============> g fBAedc
* |
* +--> dequeue for IO
*/
static void queue_io(struct bdi_writeback *wb, struct wb_writeback_work *work)
{
int moved;
assert_spin_locked(&wb->list_lock);
list_splice_init(&wb->b_more_io, &wb->b_io);
moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, work);
trace_writeback_queue_io(wb, work, moved);
}
static int write_inode(struct inode *inode, struct writeback_control *wbc)
{
int ret;
if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode)) {
trace_writeback_write_inode_start(inode, wbc);
ret = inode->i_sb->s_op->write_inode(inode, wbc);
trace_writeback_write_inode(inode, wbc);
return ret;
}
return 0;
}
/*
* Wait for writeback on an inode to complete. Called with i_lock held.
* Caller must make sure inode cannot go away when we drop i_lock.
*/
static void __inode_wait_for_writeback(struct inode *inode)
__releases(inode->i_lock)
__acquires(inode->i_lock)
{
DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
wait_queue_head_t *wqh;
wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
while (inode->i_state & I_SYNC) {
spin_unlock(&inode->i_lock);
__wait_on_bit(wqh, &wq, bit_wait,
TASK_UNINTERRUPTIBLE);
spin_lock(&inode->i_lock);
}
}
/*
* Wait for writeback on an inode to complete. Caller must have inode pinned.
*/
void inode_wait_for_writeback(struct inode *inode)
{
spin_lock(&inode->i_lock);
__inode_wait_for_writeback(inode);
spin_unlock(&inode->i_lock);
}
/*
* Sleep until I_SYNC is cleared. This function must be called with i_lock
* held and drops it. It is aimed for callers not holding any inode reference
* so once i_lock is dropped, inode can go away.
*/
static void inode_sleep_on_writeback(struct inode *inode)
__releases(inode->i_lock)
{
DEFINE_WAIT(wait);
wait_queue_head_t *wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
int sleep;
prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
sleep = inode->i_state & I_SYNC;
spin_unlock(&inode->i_lock);
if (sleep)
schedule();
finish_wait(wqh, &wait);
}
/*
* Find proper writeback list for the inode depending on its current state and
* possibly also change of its state while we were doing writeback. Here we
* handle things such as livelock prevention or fairness of writeback among
* inodes. This function can be called only by flusher thread - noone else
* processes all inodes in writeback lists and requeueing inodes behind flusher
* thread's back can have unexpected consequences.
*/
static void requeue_inode(struct inode *inode, struct bdi_writeback *wb,
struct writeback_control *wbc)
{
if (inode->i_state & I_FREEING)
return;
/*
* Sync livelock prevention. Each inode is tagged and synced in one
* shot. If still dirty, it will be redirty_tail()'ed below. Update
* the dirty time to prevent enqueue and sync it again.
*/
if ((inode->i_state & I_DIRTY) &&
(wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages))
inode->dirtied_when = jiffies;
if (wbc->pages_skipped) {
/*
* writeback is not making progress due to locked
* buffers. Skip this inode for now.
*/
redirty_tail(inode, wb);
return;
}
if (mapping_tagged(inode->i_mapping, PAGECACHE_TAG_DIRTY)) {
/*
* We didn't write back all the pages. nfs_writepages()
* sometimes bales out without doing anything.
*/
if (wbc->nr_to_write <= 0) {
/* Slice used up. Queue for next turn. */
requeue_io(inode, wb);
} else {
/*
* Writeback blocked by something other than
* congestion. Delay the inode for some time to
* avoid spinning on the CPU (100% iowait)
* retrying writeback of the dirty page/inode
* that cannot be performed immediately.
*/
redirty_tail(inode, wb);
}
} else if (inode->i_state & I_DIRTY) {
/*
* Filesystems can dirty the inode during writeback operations,
* such as delayed allocation during submission or metadata
* updates after data IO completion.
*/
redirty_tail(inode, wb);
} else {
/* The inode is clean. Remove from writeback lists. */
list_del_init(&inode->i_wb_list);
}
}
/*
* Write out an inode and its dirty pages. Do not update the writeback list
* linkage. That is left to the caller. The caller is also responsible for
* setting I_SYNC flag and calling inode_sync_complete() to clear it.
*/
static int
__writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
{
struct address_space *mapping = inode->i_mapping;
long nr_to_write = wbc->nr_to_write;
unsigned dirty;
int ret;
WARN_ON(!(inode->i_state & I_SYNC));
trace_writeback_single_inode_start(inode, wbc, nr_to_write);
ret = do_writepages(mapping, wbc);
/*
* Make sure to wait on the data before writing out the metadata.
* This is important for filesystems that modify metadata on data
* I/O completion. We don't do it for sync(2) writeback because it has a
* separate, external IO completion path and ->sync_fs for guaranteeing
* inode metadata is written back correctly.
*/
if (wbc->sync_mode == WB_SYNC_ALL && !wbc->for_sync) {
int err = filemap_fdatawait(mapping);
if (ret == 0)
ret = err;
}
/*
* Some filesystems may redirty the inode during the writeback
* due to delalloc, clear dirty metadata flags right before
* write_inode()
*/
spin_lock(&inode->i_lock);
dirty = inode->i_state & I_DIRTY;
inode->i_state &= ~I_DIRTY;
/*
* Paired with smp_mb() in __mark_inode_dirty(). This allows
* __mark_inode_dirty() to test i_state without grabbing i_lock -
* either they see the I_DIRTY bits cleared or we see the dirtied
* inode.
*
* I_DIRTY_PAGES is always cleared together above even if @mapping
* still has dirty pages. The flag is reinstated after smp_mb() if
* necessary. This guarantees that either __mark_inode_dirty()
* sees clear I_DIRTY_PAGES or we see PAGECACHE_TAG_DIRTY.
*/
smp_mb();
if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
inode->i_state |= I_DIRTY_PAGES;
spin_unlock(&inode->i_lock);
/* Don't write the inode if only I_DIRTY_PAGES was set */
if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
int err = write_inode(inode, wbc);
if (ret == 0)
ret = err;
}
trace_writeback_single_inode(inode, wbc, nr_to_write);
return ret;
}
/*
* Write out an inode's dirty pages. Either the caller has an active reference
* on the inode or the inode has I_WILL_FREE set.
*
* This function is designed to be called for writing back one inode which
* we go e.g. from filesystem. Flusher thread uses __writeback_single_inode()
* and does more profound writeback list handling in writeback_sb_inodes().
*/
static int
writeback_single_inode(struct inode *inode, struct bdi_writeback *wb,
struct writeback_control *wbc)
{
int ret = 0;
spin_lock(&inode->i_lock);
if (!atomic_read(&inode->i_count))
WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
else
WARN_ON(inode->i_state & I_WILL_FREE);
if (inode->i_state & I_SYNC) {
if (wbc->sync_mode != WB_SYNC_ALL)
goto out;
/*
* It's a data-integrity sync. We must wait. Since callers hold
* inode reference or inode has I_WILL_FREE set, it cannot go
* away under us.
*/
__inode_wait_for_writeback(inode);
}
WARN_ON(inode->i_state & I_SYNC);
/*
* Skip inode if it is clean and we have no outstanding writeback in
* WB_SYNC_ALL mode. We don't want to mess with writeback lists in this
* function since flusher thread may be doing for example sync in
* parallel and if we move the inode, it could get skipped. So here we
* make sure inode is on some writeback list and leave it there unless
* we have completely cleaned the inode.
*/
if (!(inode->i_state & I_DIRTY) &&
(wbc->sync_mode != WB_SYNC_ALL ||
!mapping_tagged(inode->i_mapping, PAGECACHE_TAG_WRITEBACK)))
goto out;
inode->i_state |= I_SYNC;
spin_unlock(&inode->i_lock);
ret = __writeback_single_inode(inode, wbc);
spin_lock(&wb->list_lock);
spin_lock(&inode->i_lock);
/*
* If inode is clean, remove it from writeback lists. Otherwise don't
* touch it. See comment above for explanation.
*/
if (!(inode->i_state & I_DIRTY))
list_del_init(&inode->i_wb_list);
spin_unlock(&wb->list_lock);
inode_sync_complete(inode);
out:
spin_unlock(&inode->i_lock);
return ret;
}
static long writeback_chunk_size(struct backing_dev_info *bdi,
struct wb_writeback_work *work)
{
long pages;
/*
* WB_SYNC_ALL mode does livelock avoidance by syncing dirty
* inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
* here avoids calling into writeback_inodes_wb() more than once.
*
* The intended call sequence for WB_SYNC_ALL writeback is:
*
* wb_writeback()
* writeback_sb_inodes() <== called only once
* write_cache_pages() <== called once for each inode
* (quickly) tag currently dirty pages
* (maybe slowly) sync all tagged pages
*/
if (work->sync_mode == WB_SYNC_ALL || work->tagged_writepages)
pages = LONG_MAX;
else {
pages = min(bdi->avg_write_bandwidth / 2,
global_dirty_limit / DIRTY_SCOPE);
pages = min(pages, work->nr_pages);
pages = round_down(pages + MIN_WRITEBACK_PAGES,
MIN_WRITEBACK_PAGES);
}
return pages;
}
/*
* Write a portion of b_io inodes which belong to @sb.
*
* Return the number of pages and/or inodes written.
*/
static long writeback_sb_inodes(struct super_block *sb,
struct bdi_writeback *wb,
struct wb_writeback_work *work)
{
struct writeback_control wbc = {
.sync_mode = work->sync_mode,
.tagged_writepages = work->tagged_writepages,
.for_kupdate = work->for_kupdate,
.for_background = work->for_background,
.for_sync = work->for_sync,
.range_cyclic = work->range_cyclic,
.range_start = 0,
.range_end = LLONG_MAX,
};
unsigned long start_time = jiffies;
long write_chunk;
long wrote = 0; /* count both pages and inodes */
while (!list_empty(&wb->b_io)) {
struct inode *inode = wb_inode(wb->b_io.prev);
if (inode->i_sb != sb) {
if (work->sb) {
/*
* We only want to write back data for this
* superblock, move all inodes not belonging
* to it back onto the dirty list.
*/
redirty_tail(inode, wb);
continue;
}
/*
* The inode belongs to a different superblock.
* Bounce back to the caller to unpin this and
* pin the next superblock.
*/
break;
}
/*
* Don't bother with new inodes or inodes being freed, first
* kind does not need periodic writeout yet, and for the latter
* kind writeout is handled by the freer.
*/
spin_lock(&inode->i_lock);
if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
spin_unlock(&inode->i_lock);
redirty_tail(inode, wb);
continue;
}
if ((inode->i_state & I_SYNC) && wbc.sync_mode != WB_SYNC_ALL) {
/*
* If this inode is locked for writeback and we are not
* doing writeback-for-data-integrity, move it to
* b_more_io so that writeback can proceed with the
* other inodes on s_io.
*
* We'll have another go at writing back this inode
* when we completed a full scan of b_io.
*/
spin_unlock(&inode->i_lock);
requeue_io(inode, wb);
trace_writeback_sb_inodes_requeue(inode);
continue;
}
spin_unlock(&wb->list_lock);
/*
* We already requeued the inode if it had I_SYNC set and we
* are doing WB_SYNC_NONE writeback. So this catches only the
* WB_SYNC_ALL case.
*/
if (inode->i_state & I_SYNC) {
/* Wait for I_SYNC. This function drops i_lock... */
inode_sleep_on_writeback(inode);
/* Inode may be gone, start again */
spin_lock(&wb->list_lock);
continue;
}
inode->i_state |= I_SYNC;
spin_unlock(&inode->i_lock);
write_chunk = writeback_chunk_size(wb->bdi, work);
wbc.nr_to_write = write_chunk;
wbc.pages_skipped = 0;
/*
* We use I_SYNC to pin the inode in memory. While it is set
* evict_inode() will wait so the inode cannot be freed.
*/
__writeback_single_inode(inode, &wbc);
work->nr_pages -= write_chunk - wbc.nr_to_write;
wrote += write_chunk - wbc.nr_to_write;
spin_lock(&wb->list_lock);
spin_lock(&inode->i_lock);
if (!(inode->i_state & I_DIRTY))
wrote++;
requeue_inode(inode, wb, &wbc);
inode_sync_complete(inode);
spin_unlock(&inode->i_lock);
cond_resched_lock(&wb->list_lock);
/*
* bail out to wb_writeback() often enough to check
* background threshold and other termination conditions.
*/
if (wrote) {
if (time_is_before_jiffies(start_time + HZ / 10UL))
break;
if (work->nr_pages <= 0)
break;
}
}
return wrote;
}
static long __writeback_inodes_wb(struct bdi_writeback *wb,
struct wb_writeback_work *work)
{
unsigned long start_time = jiffies;
long wrote = 0;
while (!list_empty(&wb->b_io)) {
struct inode *inode = wb_inode(wb->b_io.prev);
struct super_block *sb = inode->i_sb;
if (!grab_super_passive(sb)) {
/*
* grab_super_passive() may fail consistently due to
* s_umount being grabbed by someone else. Don't use
* requeue_io() to avoid busy retrying the inode/sb.
*/
redirty_tail(inode, wb);
continue;
}
wrote += writeback_sb_inodes(sb, wb, work);
drop_super(sb);
/* refer to the same tests at the end of writeback_sb_inodes */
if (wrote) {
if (time_is_before_jiffies(start_time + HZ / 10UL))
break;
if (work->nr_pages <= 0)
break;
}
}
/* Leave any unwritten inodes on b_io */
return wrote;
}
static long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
enum wb_reason reason)
{
struct wb_writeback_work work = {
.nr_pages = nr_pages,
.sync_mode = WB_SYNC_NONE,
.range_cyclic = 1,
.reason = reason,
};
spin_lock(&wb->list_lock);
if (list_empty(&wb->b_io))
queue_io(wb, &work);
__writeback_inodes_wb(wb, &work);
spin_unlock(&wb->list_lock);
return nr_pages - work.nr_pages;
}
static bool over_bground_thresh(struct backing_dev_info *bdi)
{
unsigned long background_thresh, dirty_thresh;
global_dirty_limits(&background_thresh, &dirty_thresh);
if (global_page_state(NR_FILE_DIRTY) +
global_page_state(NR_UNSTABLE_NFS) > background_thresh)
return true;
if (bdi_stat(bdi, BDI_RECLAIMABLE) >
bdi_dirty_limit(bdi, background_thresh))
return true;
return false;
}
/*
* Called under wb->list_lock. If there are multiple wb per bdi,
* only the flusher working on the first wb should do it.
*/
static void wb_update_bandwidth(struct bdi_writeback *wb,
unsigned long start_time)
{
__bdi_update_bandwidth(wb->bdi, 0, 0, 0, 0, 0, start_time);
}
/*
* Explicit flushing or periodic writeback of "old" data.
*
* Define "old": the first time one of an inode's pages is dirtied, we mark the
* dirtying-time in the inode's address_space. So this periodic writeback code
* just walks the superblock inode list, writing back any inodes which are
* older than a specific point in time.
*
* Try to run once per dirty_writeback_interval. But if a writeback event
* takes longer than a dirty_writeback_interval interval, then leave a
* one-second gap.
*
* older_than_this takes precedence over nr_to_write. So we'll only write back
* all dirty pages if they are all attached to "old" mappings.
*/
static long wb_writeback(struct bdi_writeback *wb,
struct wb_writeback_work *work)
{
unsigned long wb_start = jiffies;
long nr_pages = work->nr_pages;
unsigned long oldest_jif;
struct inode *inode;
long progress;
oldest_jif = jiffies;
work->older_than_this = &oldest_jif;
spin_lock(&wb->list_lock);
for (;;) {
/*
* Stop writeback when nr_pages has been consumed
*/
if (work->nr_pages <= 0)
break;
/*
* Background writeout and kupdate-style writeback may
* run forever. Stop them if there is other work to do
* so that e.g. sync can proceed. They'll be restarted
* after the other works are all done.
*/
if ((work->for_background || work->for_kupdate) &&
!list_empty(&wb->bdi->work_list))
break;
/*
* For background writeout, stop when we are below the
* background dirty threshold
*/
if (work->for_background && !over_bground_thresh(wb->bdi))
break;
/*
* Kupdate and background works are special and we want to
* include all inodes that need writing. Livelock avoidance is
* handled by these works yielding to any other work so we are
* safe.
*/
if (work->for_kupdate) {
oldest_jif = jiffies -
msecs_to_jiffies(dirty_expire_interval * 10);
} else if (work->for_background)
oldest_jif = jiffies;
trace_writeback_start(wb->bdi, work);
if (list_empty(&wb->b_io))
queue_io(wb, work);
if (work->sb)
progress = writeback_sb_inodes(work->sb, wb, work);
else
progress = __writeback_inodes_wb(wb, work);
trace_writeback_written(wb->bdi, work);
wb_update_bandwidth(wb, wb_start);
/*
* Did we write something? Try for more
*
* Dirty inodes are moved to b_io for writeback in batches.
* The completion of the current batch does not necessarily
* mean the overall work is done. So we keep looping as long
* as made some progress on cleaning pages or inodes.
*/
if (progress)
continue;
/*
* No more inodes for IO, bail
*/
if (list_empty(&wb->b_more_io))
break;
/*
* Nothing written. Wait for some inode to
* become available for writeback. Otherwise
* we'll just busyloop.
*/
if (!list_empty(&wb->b_more_io)) {
trace_writeback_wait(wb->bdi, work);
inode = wb_inode(wb->b_more_io.prev);
spin_lock(&inode->i_lock);
spin_unlock(&wb->list_lock);
/* This function drops i_lock... */
inode_sleep_on_writeback(inode);
spin_lock(&wb->list_lock);
}
}
spin_unlock(&wb->list_lock);
return nr_pages - work->nr_pages;
}
/*
* Return the next wb_writeback_work struct that hasn't been processed yet.
*/
static struct wb_writeback_work *
get_next_work_item(struct backing_dev_info *bdi)
{
struct wb_writeback_work *work = NULL;
spin_lock_bh(&bdi->wb_lock);
if (!list_empty(&bdi->work_list)) {
work = list_entry(bdi->work_list.next,
struct wb_writeback_work, list);
list_del_init(&work->list);
}
spin_unlock_bh(&bdi->wb_lock);
return work;
}
/*
* Add in the number of potentially dirty inodes, because each inode
* write can dirty pagecache in the underlying blockdev.
*/
static unsigned long get_nr_dirty_pages(void)
{
return global_page_state(NR_FILE_DIRTY) +
global_page_state(NR_UNSTABLE_NFS) +
get_nr_dirty_inodes();
}
static long wb_check_background_flush(struct bdi_writeback *wb)
{
if (over_bground_thresh(wb->bdi)) {
struct wb_writeback_work work = {
.nr_pages = LONG_MAX,
.sync_mode = WB_SYNC_NONE,
.for_background = 1,
.range_cyclic = 1,
.reason = WB_REASON_BACKGROUND,
};
return wb_writeback(wb, &work);
}
return 0;
}
static long wb_check_old_data_flush(struct bdi_writeback *wb)
{
unsigned long expired;
long nr_pages;
/*
* When set to zero, disable periodic writeback
*/
if (!dirty_writeback_interval)
return 0;
expired = wb->last_old_flush +
msecs_to_jiffies(dirty_writeback_interval * 10);
if (time_before(jiffies, expired))
return 0;
wb->last_old_flush = jiffies;
nr_pages = get_nr_dirty_pages();
if (nr_pages) {
struct wb_writeback_work work = {
.nr_pages = nr_pages,
.sync_mode = WB_SYNC_NONE,
.for_kupdate = 1,
.range_cyclic = 1,
.reason = WB_REASON_PERIODIC,
};
return wb_writeback(wb, &work);
}
return 0;
}
/*
* Retrieve work items and do the writeback they describe
*/
static long wb_do_writeback(struct bdi_writeback *wb)
{
struct backing_dev_info *bdi = wb->bdi;
struct wb_writeback_work *work;
long wrote = 0;
set_bit(BDI_writeback_running, &wb->bdi->state);
while ((work = get_next_work_item(bdi)) != NULL) {
trace_writeback_exec(bdi, work);
wrote += wb_writeback(wb, work);
/*
* Notify the caller of completion if this is a synchronous
* work item, otherwise just free it.
*/
if (work->done)
complete(work->done);
else
kfree(work);
}
/*
* Check for periodic writeback, kupdated() style
*/
wrote += wb_check_old_data_flush(wb);
wrote += wb_check_background_flush(wb);
clear_bit(BDI_writeback_running, &wb->bdi->state);
return wrote;
}
/*
* Handle writeback of dirty data for the device backed by this bdi. Also
* reschedules periodically and does kupdated style flushing.
*/
void bdi_writeback_workfn(struct work_struct *work)
{
struct bdi_writeback *wb = container_of(to_delayed_work(work),
struct bdi_writeback, dwork);
struct backing_dev_info *bdi = wb->bdi;
long pages_written;
set_worker_desc("flush-%s", dev_name(bdi->dev));
current->flags |= PF_SWAPWRITE;
if (likely(!current_is_workqueue_rescuer() ||
!test_bit(BDI_registered, &bdi->state))) {
/*
* The normal path. Keep writing back @bdi until its
* work_list is empty. Note that this path is also taken
* if @bdi is shutting down even when we're running off the
* rescuer as work_list needs to be drained.
*/
do {
pages_written = wb_do_writeback(wb);
trace_writeback_pages_written(pages_written);
} while (!list_empty(&bdi->work_list));
} else {
/*
* bdi_wq can't get enough workers and we're running off
* the emergency worker. Don't hog it. Hopefully, 1024 is
* enough for efficient IO.
*/
pages_written = writeback_inodes_wb(&bdi->wb, 1024,
WB_REASON_FORKER_THREAD);
trace_writeback_pages_written(pages_written);
}
if (!list_empty(&bdi->work_list))
mod_delayed_work(bdi_wq, &wb->dwork, 0);
else if (wb_has_dirty_io(wb) && dirty_writeback_interval)
bdi_wakeup_thread_delayed(bdi);
current->flags &= ~PF_SWAPWRITE;
}
/*
* Start writeback of `nr_pages' pages. If `nr_pages' is zero, write back
* the whole world.
*/
void wakeup_flusher_threads(long nr_pages, enum wb_reason reason)
{
struct backing_dev_info *bdi;
if (!nr_pages)
nr_pages = get_nr_dirty_pages();
rcu_read_lock();
list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
if (!bdi_has_dirty_io(bdi))
continue;
__bdi_start_writeback(bdi, nr_pages, false, reason);
}
rcu_read_unlock();
}
static noinline void block_dump___mark_inode_dirty(struct inode *inode)
{
if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) {
struct dentry *dentry;
const char *name = "?";
dentry = d_find_alias(inode);
if (dentry) {
spin_lock(&dentry->d_lock);
name = (const char *) dentry->d_name.name;
}
printk(KERN_DEBUG
"%s(%d): dirtied inode %lu (%s) on %s\n",
current->comm, task_pid_nr(current), inode->i_ino,
name, inode->i_sb->s_id);
if (dentry) {
spin_unlock(&dentry->d_lock);
dput(dentry);
}
}
}
/**
* __mark_inode_dirty - internal function
* @inode: inode to mark
* @flags: what kind of dirty (i.e. I_DIRTY_SYNC)
* Mark an inode as dirty. Callers should use mark_inode_dirty or
* mark_inode_dirty_sync.
*
* Put the inode on the super block's dirty list.
*
* CAREFUL! We mark it dirty unconditionally, but move it onto the
* dirty list only if it is hashed or if it refers to a blockdev.
* If it was not hashed, it will never be added to the dirty list
* even if it is later hashed, as it will have been marked dirty already.
*
* In short, make sure you hash any inodes _before_ you start marking
* them dirty.
*
* Note that for blockdevs, inode->dirtied_when represents the dirtying time of
* the block-special inode (/dev/hda1) itself. And the ->dirtied_when field of
* the kernel-internal blockdev inode represents the dirtying time of the
* blockdev's pages. This is why for I_DIRTY_PAGES we always use
* page->mapping->host, so the page-dirtying time is recorded in the internal
* blockdev inode.
*/
void __mark_inode_dirty(struct inode *inode, int flags)
{
struct super_block *sb = inode->i_sb;
struct backing_dev_info *bdi = NULL;
/*
* Don't do this for I_DIRTY_PAGES - that doesn't actually
* dirty the inode itself
*/
if (flags & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
trace_writeback_dirty_inode_start(inode, flags);
if (sb->s_op->dirty_inode)
sb->s_op->dirty_inode(inode, flags);
trace_writeback_dirty_inode(inode, flags);
}
/*
* Paired with smp_mb() in __writeback_single_inode() for the
* following lockless i_state test. See there for details.
*/
smp_mb();
if ((inode->i_state & flags) == flags)
return;
if (unlikely(block_dump))
block_dump___mark_inode_dirty(inode);
spin_lock(&inode->i_lock);
if ((inode->i_state & flags) != flags) {
const int was_dirty = inode->i_state & I_DIRTY;
inode->i_state |= flags;
/*
* If the inode is being synced, just update its dirty state.
* The unlocker will place the inode on the appropriate
* superblock list, based upon its state.
*/
if (inode->i_state & I_SYNC)
goto out_unlock_inode;
/*
* Only add valid (hashed) inodes to the superblock's
* dirty list. Add blockdev inodes as well.
*/
if (!S_ISBLK(inode->i_mode)) {
if (inode_unhashed(inode))
goto out_unlock_inode;
}
if (inode->i_state & I_FREEING)
goto out_unlock_inode;
/*
* If the inode was already on b_dirty/b_io/b_more_io, don't
* reposition it (that would break b_dirty time-ordering).
*/
if (!was_dirty) {
bool wakeup_bdi = false;
bdi = inode_to_bdi(inode);
spin_unlock(&inode->i_lock);
spin_lock(&bdi->wb.list_lock);
if (bdi_cap_writeback_dirty(bdi)) {
WARN(!test_bit(BDI_registered, &bdi->state),
"bdi-%s not registered\n", bdi->name);
/*
* If this is the first dirty inode for this
* bdi, we have to wake-up the corresponding
* bdi thread to make sure background
* write-back happens later.
*/
if (!wb_has_dirty_io(&bdi->wb))
wakeup_bdi = true;
}
inode->dirtied_when = jiffies;
list_move(&inode->i_wb_list, &bdi->wb.b_dirty);
spin_unlock(&bdi->wb.list_lock);
if (wakeup_bdi)
bdi_wakeup_thread_delayed(bdi);
return;
}
}
out_unlock_inode:
spin_unlock(&inode->i_lock);
}
EXPORT_SYMBOL(__mark_inode_dirty);
static void wait_sb_inodes(struct super_block *sb)
{
struct inode *inode, *old_inode = NULL;
/*
* We need to be protected against the filesystem going from
* r/o to r/w or vice versa.
*/
WARN_ON(!rwsem_is_locked(&sb->s_umount));
spin_lock(&inode_sb_list_lock);
/*
* Data integrity sync. Must wait for all pages under writeback,
* because there may have been pages dirtied before our sync
* call, but which had writeout started before we write it out.
* In which case, the inode may not be on the dirty list, but
* we still have to wait for that writeout.
*/
list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
struct address_space *mapping = inode->i_mapping;
spin_lock(&inode->i_lock);
if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
(mapping->nrpages == 0)) {
spin_unlock(&inode->i_lock);
continue;
}
__iget(inode);
spin_unlock(&inode->i_lock);
spin_unlock(&inode_sb_list_lock);
/*
* We hold a reference to 'inode' so it couldn't have been
* removed from s_inodes list while we dropped the
* inode_sb_list_lock. We cannot iput the inode now as we can
* be holding the last reference and we cannot iput it under
* inode_sb_list_lock. So we keep the reference and iput it
* later.
*/
iput(old_inode);
old_inode = inode;
filemap_fdatawait(mapping);
cond_resched();
spin_lock(&inode_sb_list_lock);
}
spin_unlock(&inode_sb_list_lock);
iput(old_inode);
}
/**
* writeback_inodes_sb_nr - writeback dirty inodes from given super_block
* @sb: the superblock
* @nr: the number of pages to write
* @reason: reason why some writeback work initiated
*
* Start writeback on some inodes on this super_block. No guarantees are made
* on how many (if any) will be written, and this function does not wait
* for IO completion of submitted IO.
*/
void writeback_inodes_sb_nr(struct super_block *sb,
unsigned long nr,
enum wb_reason reason)
{
DECLARE_COMPLETION_ONSTACK(done);
struct wb_writeback_work work = {
.sb = sb,
.sync_mode = WB_SYNC_NONE,
.tagged_writepages = 1,
.done = &done,
.nr_pages = nr,
.reason = reason,
};
if (sb->s_bdi == &noop_backing_dev_info)
return;
WARN_ON(!rwsem_is_locked(&sb->s_umount));
bdi_queue_work(sb->s_bdi, &work);
wait_for_completion(&done);
}
EXPORT_SYMBOL(writeback_inodes_sb_nr);
/**
* writeback_inodes_sb - writeback dirty inodes from given super_block
* @sb: the superblock
* @reason: reason why some writeback work was initiated
*
* Start writeback on some inodes on this super_block. No guarantees are made
* on how many (if any) will be written, and this function does not wait
* for IO completion of submitted IO.
*/
void writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
{
return writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
}
EXPORT_SYMBOL(writeback_inodes_sb);
/**
* try_to_writeback_inodes_sb_nr - try to start writeback if none underway
* @sb: the superblock
* @nr: the number of pages to write
* @reason: the reason of writeback
*
* Invoke writeback_inodes_sb_nr if no writeback is currently underway.
* Returns 1 if writeback was started, 0 if not.
*/
int try_to_writeback_inodes_sb_nr(struct super_block *sb,
unsigned long nr,
enum wb_reason reason)
{
if (writeback_in_progress(sb->s_bdi))
return 1;
if (!down_read_trylock(&sb->s_umount))
return 0;
writeback_inodes_sb_nr(sb, nr, reason);
up_read(&sb->s_umount);
return 1;
}
EXPORT_SYMBOL(try_to_writeback_inodes_sb_nr);
/**
* try_to_writeback_inodes_sb - try to start writeback if none underway
* @sb: the superblock
* @reason: reason why some writeback work was initiated
*
* Implement by try_to_writeback_inodes_sb_nr()
* Returns 1 if writeback was started, 0 if not.
*/
int try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
{
return try_to_writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
}
EXPORT_SYMBOL(try_to_writeback_inodes_sb);
/**
* sync_inodes_sb - sync sb inode pages
* @sb: the superblock
*
* This function writes and waits on any dirty inode belonging to this
* super_block.
*/
void sync_inodes_sb(struct super_block *sb)
{
DECLARE_COMPLETION_ONSTACK(done);
struct wb_writeback_work work = {
.sb = sb,
.sync_mode = WB_SYNC_ALL,
.nr_pages = LONG_MAX,
.range_cyclic = 0,
.done = &done,
.reason = WB_REASON_SYNC,
.for_sync = 1,
};
/* Nothing to do? */
if (sb->s_bdi == &noop_backing_dev_info)
return;
WARN_ON(!rwsem_is_locked(&sb->s_umount));
bdi_queue_work(sb->s_bdi, &work);
wait_for_completion(&done);
wait_sb_inodes(sb);
}
EXPORT_SYMBOL(sync_inodes_sb);
/**
* write_inode_now - write an inode to disk
* @inode: inode to write to disk
* @sync: whether the write should be synchronous or not
*
* This function commits an inode to disk immediately if it is dirty. This is
* primarily needed by knfsd.
*
* The caller must either have a ref on the inode or must have set I_WILL_FREE.
*/
int write_inode_now(struct inode *inode, int sync)
{
struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
struct writeback_control wbc = {
.nr_to_write = LONG_MAX,
.sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
.range_start = 0,
.range_end = LLONG_MAX,
};
if (!mapping_cap_writeback_dirty(inode->i_mapping))
wbc.nr_to_write = 0;
might_sleep();
return writeback_single_inode(inode, wb, &wbc);
}
EXPORT_SYMBOL(write_inode_now);
/**
* sync_inode - write an inode and its pages to disk.
* @inode: the inode to sync
* @wbc: controls the writeback mode
*
* sync_inode() will write an inode and its pages to disk. It will also
* correctly update the inode on its superblock's dirty inode lists and will
* update inode->i_state.
*
* The caller must have a ref on the inode.
*/
int sync_inode(struct inode *inode, struct writeback_control *wbc)
{
return writeback_single_inode(inode, &inode_to_bdi(inode)->wb, wbc);
}
EXPORT_SYMBOL(sync_inode);
/**
* sync_inode_metadata - write an inode to disk
* @inode: the inode to sync
* @wait: wait for I/O to complete.
*
* Write an inode to disk and adjust its dirty state after completion.
*
* Note: only writes the actual inode, no associated data or other metadata.
*/
int sync_inode_metadata(struct inode *inode, int wait)
{
struct writeback_control wbc = {
.sync_mode = wait ? WB_SYNC_ALL : WB_SYNC_NONE,
.nr_to_write = 0, /* metadata-only */
};
return sync_inode(inode, &wbc);
}
EXPORT_SYMBOL(sync_inode_metadata);