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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
839a8e8660
("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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
parent
2dbecc73f3
commit
39305a6ac7
2 changed files with 8 additions and 5 deletions
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@ -1038,10 +1038,10 @@ void bdi_writeback_workfn(struct work_struct *work)
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trace_writeback_pages_written(pages_written);
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}
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if (!list_empty(&bdi->work_list) ||
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(wb_has_dirty_io(wb) && dirty_writeback_interval))
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queue_delayed_work(bdi_wq, &wb->dwork,
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msecs_to_jiffies(dirty_writeback_interval * 10));
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if (!list_empty(&bdi->work_list))
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mod_delayed_work(bdi_wq, &wb->dwork, 0);
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else if (wb_has_dirty_io(wb) && dirty_writeback_interval)
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bdi_wakeup_thread_delayed(bdi);
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current->flags &= ~PF_SWAPWRITE;
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}
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@ -287,13 +287,16 @@ int bdi_has_dirty_io(struct backing_dev_info *bdi)
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* Note, we wouldn't bother setting up the timer, but this function is on the
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* fast-path (used by '__mark_inode_dirty()'), so we save few context switches
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* by delaying the wake-up.
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*
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* We have to be careful not to postpone flush work if it is scheduled for
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* earlier. Thus we use queue_delayed_work().
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*/
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void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi)
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{
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unsigned long timeout;
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timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
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mod_delayed_work(bdi_wq, &bdi->wb.dwork, timeout);
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queue_delayed_work(bdi_wq, &bdi->wb.dwork, timeout);
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}
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/*
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