Commit 6ca738d60c563d5c6cf6253ee4b8e76fa77b2b9e
Committed by
Linus Torvalds
1 parent
a0c32761e7
Exists in
master
and in
13 other branches
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>
Showing 2 changed files with 8 additions and 5 deletions Side-by-side Diff
fs/fs-writeback.c
... | ... | @@ -1039,10 +1039,10 @@ |
1039 | 1039 | trace_writeback_pages_written(pages_written); |
1040 | 1040 | } |
1041 | 1041 | |
1042 | - if (!list_empty(&bdi->work_list) || | |
1043 | - (wb_has_dirty_io(wb) && dirty_writeback_interval)) | |
1044 | - queue_delayed_work(bdi_wq, &wb->dwork, | |
1045 | - msecs_to_jiffies(dirty_writeback_interval * 10)); | |
1042 | + if (!list_empty(&bdi->work_list)) | |
1043 | + mod_delayed_work(bdi_wq, &wb->dwork, 0); | |
1044 | + else if (wb_has_dirty_io(wb) && dirty_writeback_interval) | |
1045 | + bdi_wakeup_thread_delayed(bdi); | |
1046 | 1046 | |
1047 | 1047 | current->flags &= ~PF_SWAPWRITE; |
1048 | 1048 | } |
mm/backing-dev.c
... | ... | @@ -288,13 +288,16 @@ |
288 | 288 | * Note, we wouldn't bother setting up the timer, but this function is on the |
289 | 289 | * fast-path (used by '__mark_inode_dirty()'), so we save few context switches |
290 | 290 | * by delaying the wake-up. |
291 | + * | |
292 | + * We have to be careful not to postpone flush work if it is scheduled for | |
293 | + * earlier. Thus we use queue_delayed_work(). | |
291 | 294 | */ |
292 | 295 | void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi) |
293 | 296 | { |
294 | 297 | unsigned long timeout; |
295 | 298 | |
296 | 299 | timeout = msecs_to_jiffies(dirty_writeback_interval * 10); |
297 | - mod_delayed_work(bdi_wq, &bdi->wb.dwork, timeout); | |
300 | + queue_delayed_work(bdi_wq, &bdi->wb.dwork, timeout); | |
298 | 301 | } |
299 | 302 | |
300 | 303 | /* |