From: Jeff Moyer <jmoyer@redhat.com>
To: Jan Kara <jack@suse.cz>
Cc: LKML <linux-kernel@vger.kernel.org>,
linux-fsdevel@vger.kernel.org, Tejun Heo <tj@kernel.org>,
Jens Axboe <jaxboe@fusionio.com>
Subject: Re: Deadlocks due to per-process plugging
Date: Wed, 11 Jul 2012 12:05:51 -0400 [thread overview]
Message-ID: <x49ehoii8ps.fsf@segfault.boston.devel.redhat.com> (raw)
In-Reply-To: <20120711133735.GA8122@quack.suse.cz> (Jan Kara's message of "Wed, 11 Jul 2012 15:37:35 +0200")
Jan Kara <jack@suse.cz> writes:
> Hello,
>
> we've recently hit a deadlock in our QA runs which is caused by the
> per-process plugging code. The problem is as follows:
> process A process B (kjournald)
> generic_file_aio_write()
> blk_start_plug(&plug);
> ...
> somewhere in here we allocate memory and
> direct reclaim submits buffer X for IO
> ...
> ext3_write_begin()
> ext3_journal_start()
> we need more space in a journal
> so we want to checkpoint old transactions,
> we block waiting for kjournald to commit
> a currently running transaction.
> journal_commit_transaction()
> wait for IO on buffer X
> to complete as it is part
> of the current transaction
>
> => deadlock since A waits for B and B waits for A to do unplug.
> BTW: I don't think this is really ext3/ext4 specific. I think other
> filesystems can get into problems as well when direct reclaim submits some
> IO and the process subsequently blocks without submitting the IO.
So, I thought schedule would do the flush. Checking the code:
asmlinkage void __sched schedule(void)
{
struct task_struct *tsk = current;
sched_submit_work(tsk);
__schedule();
}
And sched_submit_work looks like this:
static inline void sched_submit_work(struct task_struct *tsk)
{
if (!tsk->state || tsk_is_pi_blocked(tsk))
return;
/*
* If we are going to sleep and we have plugged IO queued,
* make sure to submit it to avoid deadlocks.
*/
if (blk_needs_flush_plug(tsk))
blk_schedule_flush_plug(tsk);
}
This eventually ends in a call to blk_run_queue_async(q) after
submitting the I/O from the plug list. Right? So is the question
really why doesn't the kblockd workqueue get scheduled?
Cheers,
Jeff
next prev parent reply other threads:[~2012-07-11 16:05 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-07-11 13:37 Deadlocks due to per-process plugging Jan Kara
2012-07-11 16:05 ` Jeff Moyer [this message]
2012-07-11 20:16 ` Jan Kara
2012-07-11 22:12 ` Thomas Gleixner
2012-07-12 4:12 ` Mike Galbraith
2012-07-13 12:38 ` Jan Kara
2012-07-12 2:07 ` Mike Galbraith
2012-07-12 14:15 ` Thomas Gleixner
2012-07-13 12:33 ` Jan Kara
2012-07-13 14:25 ` Thomas Gleixner
2012-07-13 14:46 ` Jan Kara
2012-07-15 8:59 ` Thomas Gleixner
2012-07-15 9:14 ` Mike Galbraith
2012-07-15 9:51 ` Thomas Gleixner
2012-07-16 2:22 ` Mike Galbraith
2012-07-16 8:59 ` Thomas Gleixner
2012-07-16 9:48 ` Mike Galbraith
2012-07-16 9:59 ` Thomas Gleixner
2012-07-16 10:13 ` Mike Galbraith
2012-07-16 10:08 ` Mike Galbraith
2012-07-16 10:19 ` Thomas Gleixner
2012-07-16 10:30 ` Mike Galbraith
2012-07-16 11:24 ` Mike Galbraith
2012-07-16 14:35 ` Mike Galbraith
2012-07-17 13:10 ` Mike Galbraith
2012-07-18 4:44 ` Mike Galbraith
2012-07-18 5:30 ` Mike Galbraith
2012-07-21 7:47 ` Mike Galbraith
2012-07-22 18:43 ` Mike Galbraith
2012-07-23 9:46 ` Mike Galbraith
2012-07-14 11:00 ` Mike Galbraith
2012-07-14 11:06 ` Mike Galbraith
2012-07-15 7:14 ` Mike Galbraith
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