@@ -1036,10 +1036,10 @@ void bdi_writeback_workfn(struct work_struct *work)
trace_writeback_pages_written(pages_written);
}
- 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));
+ if (!list_empty(&bdi->work_list))
+ mod_delayed_work(bdi_wq, &wb->dwork, 0);
+ else if (wb_has_dirty_io(wb) && dirty_writeback_interval)
+ bdi_wakeup_thread_delayed(bdi);
current->flags &= ~PF_SWAPWRITE;
}
@@ -285,13 +285,16 @@ 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);
}
/*
This is a note to let you know that I have just added a patch titled backing_dev: fix hung task on sync to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree which can be found at: http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.11.y.z tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Luis ------ From 63f455b2b8410deb4c43def69ff885c6fad90cea Mon Sep 17 00:00:00 2001 From: Derek Basehore <dbasehore@chromium.org> Date: Thu, 3 Apr 2014 14:46:22 -0700 Subject: 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> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- fs/fs-writeback.c | 8 ++++---- mm/backing-dev.c | 5 ++++- 2 files changed, 8 insertions(+), 5 deletions(-) -- 1.9.1