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author | Derek Basehore <dbasehore@chromium.org> | 2014-04-03 23:46:22 +0200 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2014-04-04 01:20:49 +0200 |
commit | 6ca738d60c563d5c6cf6253ee4b8e76fa77b2b9e (patch) | |
tree | 916ff20799200fa096d6e6d757d2755fb53b6f17 /mm/backing-dev.c | |
parent | sh: fix format string bug in stack tracer (diff) | |
download | linux-6ca738d60c563d5c6cf6253ee4b8e76fa77b2b9e.tar.xz linux-6ca738d60c563d5c6cf6253ee4b8e76fa77b2b9e.zip |
backing_dev: fix hung task on sync
bdi_wakeup_thread_delayed() used the mod_delayed_work() function to
schedule work to writeback dirty inodes. The problem with this is that
it can delay work that is scheduled for immediate execution, such as the
work from sync_inodes_sb(). This can happen since mod_delayed_work()
can now steal work from a work_queue. This fixes the problem by using
queue_delayed_work() instead. This is a regression caused by commit
839a8e8660b6 ("writeback: replace custom worker pool implementation with
unbound workqueue").
The reason that this causes a problem is that laptop-mode will change
the delay, dirty_writeback_centisecs, to 60000 (10 minutes) by default.
In the case that bdi_wakeup_thread_delayed() races with
sync_inodes_sb(), sync will be stopped for 10 minutes and trigger a hung
task. Even if dirty_writeback_centisecs is not long enough to cause a
hung task, we still don't want to delay sync for that long.
We fix the problem by using queue_delayed_work() when we want to
schedule writeback sometime in future. This function doesn't change the
timer if it is already armed.
For the same reason, we also change bdi_writeback_workfn() to
immediately queue the work again in the case that the work_list is not
empty. The same problem can happen if the sync work is run on the
rescue worker.
[jack@suse.cz: update changelog, add comment, use bdi_wakeup_thread_delayed()]
Signed-off-by: Derek Basehore <dbasehore@chromium.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Alexander Viro <viro@zento.linux.org.uk>
Reviewed-by: Tejun Heo <tj@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: Derek Basehore <dbasehore@chromium.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Benson Leung <bleung@chromium.org>
Cc: Sonny Rao <sonnyrao@chromium.org>
Cc: Luigi Semenzato <semenzato@chromium.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Dave Chinner <david@fromorbit.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/backing-dev.c')
-rw-r--r-- | mm/backing-dev.c | 5 |
1 files changed, 4 insertions, 1 deletions
diff --git a/mm/backing-dev.c b/mm/backing-dev.c index ce682f7a4f29..fab8401fc54e 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -288,13 +288,16 @@ int bdi_has_dirty_io(struct backing_dev_info *bdi) * Note, we wouldn't bother setting up the timer, but this function is on the * fast-path (used by '__mark_inode_dirty()'), so we save few context switches * by delaying the wake-up. + * + * We have to be careful not to postpone flush work if it is scheduled for + * earlier. Thus we use queue_delayed_work(). */ void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi) { unsigned long timeout; timeout = msecs_to_jiffies(dirty_writeback_interval * 10); - mod_delayed_work(bdi_wq, &bdi->wb.dwork, timeout); + queue_delayed_work(bdi_wq, &bdi->wb.dwork, timeout); } /* |