Subject: + writeback-fix-race-that-cause-writeback-hung.patch added to -mm tree
To: junxiao.bi@xxxxxxxxxx,fengguang.wu@xxxxxxxxx,jack@xxxxxxx
From: akpm@xxxxxxxxxxxxxxxxxxxx
Date: Thu, 29 Aug 2013 12:14:50 -0700
The patch titled
Subject: writeback: fix race that cause writeback hung
has been added to the -mm tree. Its filename is
writeback-fix-race-that-cause-writeback-hung.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/writeback-fix-race-that-cause-writeback-hung.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/writeback-fix-race-that-cause-writeback-hung.patch
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From: Junxiao Bi <junxiao.bi@xxxxxxxxxx>
Subject: writeback: fix race that cause writeback hung
There is a race between mark inode dirty and writeback thread, see the
following scenario. In this case, writeback thread will not run though
there is dirty_io.
__mark_inode_dirty() bdi_writeback_workfn()
... ...
spin_lock(&inode->i_lock);
...
if (bdi_cap_writeback_dirty(bdi)) {
<<< assume wb has dirty_io, so wakeup_bdi is false.
<<< the following inode_dirty also have wakeup_bdi false.
if (!wb_has_dirty_io(&bdi->wb))
wakeup_bdi = true;
}
spin_unlock(&inode->i_lock);
<<< assume last dirty_io is removed here.
pages_written = wb_do_writeback(wb);
...
<<< work_list empty and wb has no dirty_io,
<<< delayed_work will not be queued.
if (!list_empty(&bdi->work_list) ||
(wb_has_dirty_io(wb) && dirty_writeback_interval))
queue_delayed_work(bdi_wq, &wb->dwork,
msecs_to_jiffies(dirty_writeback_interval * 10));
spin_lock(&bdi->wb.list_lock);
inode->dirtied_when = jiffies;
<<< new dirty_io is added.
list_move(&inode->i_wb_list, &bdi->wb.b_dirty);
spin_unlock(&bdi->wb.list_lock);
<<< though there is dirty_io, but wakeup_bdi is false,
<<< so writeback thread will not be waked up and
<<< the new dirty_io will not be flushed.
if (wakeup_bdi)
bdi_wakeup_thread_delayed(bdi);
Writeback will run until there is a new flush work queued. This may cause
a lot of dirty pages stay in memory for a long time.
Signed-off-by: Junxiao Bi <junxiao.bi@xxxxxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
Cc: Fengguang Wu <fengguang.wu@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/fs-writeback.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff -puN fs/fs-writeback.c~writeback-fix-race-that-cause-writeback-hung fs/fs-writeback.c
--- a/fs/fs-writeback.c~writeback-fix-race-that-cause-writeback-hung
+++ a/fs/fs-writeback.c
@@ -1171,6 +1171,8 @@ void __mark_inode_dirty(struct inode *in
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);
@@ -1185,8 +1187,6 @@ void __mark_inode_dirty(struct inode *in
wakeup_bdi = true;
}
- spin_unlock(&inode->i_lock);
- spin_lock(&bdi->wb.list_lock);
inode->dirtied_when = jiffies;
list_move(&inode->i_wb_list, &bdi->wb.b_dirty);
spin_unlock(&bdi->wb.list_lock);
_
Patches currently in -mm which might be from junxiao.bi@xxxxxxxxxx are
ocfs2-update-inode-size-after-zeronig-the-hole.patch
ocfs2-using-i_size_read-to-access-i_size.patch
writeback-fix-race-that-cause-writeback-hung.patch
linux-next.patch
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