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authorDerek Basehore <dbasehore@chromium.org>2014-04-03 14:46:22 -0700
committerJiri Slaby <jslaby@suse.cz>2014-05-05 13:36:26 +0200
commit24239843f9734736d15bc22003a3c2467b7f0fb1 (patch)
tree17a35866ef4a614c79d78bdb90fc9294e316d992 /mm
parenta9600ec90a49b7d1560f1e35fb83ead94f793b5b (diff)
backing_dev: fix hung task on sync
commit 6ca738d60c563d5c6cf6253ee4b8e76fa77b2b9e upstream. 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> Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Diffstat (limited to 'mm')
-rw-r--r--mm/backing-dev.c5
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);
}
/*