linux-kernel - Re: timer code oops when calling mod_delayed

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Message-ID: <20151103225405.GG5749@mtj.duckdns.org>
Date:	Tue, 3 Nov 2015 17:54:05 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Jeff Layton <jlayton@...chiereds.net>
Cc:	Chris Worley <chris.worley@...marydata.com>,
	linux-kernel@...r.kernel.org, bfields@...ldses.org,
	Michael Skralivetsky <michael.skralivetsky@...marydata.com>,
	Trond Myklebust <trond.myklebust@...marydata.com>,
	Shaohua Li <shli@...com>
Subject: Re: timer code oops when calling mod_delayed_work

Hello, Jeff.

On Tue, Nov 03, 2015 at 12:55:04PM -0500, Jeff Layton wrote:
> > Ok, I built a kernel with that patch reverted and that seems to fix the
> > problem.
> > 
> > Looking at the patch, I guess the main difference is that we're no
> > longer using add_timer for unbound workqueue tasks. That said, we
> > should have possession of the PENDING bit before calling add_timer_on.
> > 
> > So...I'm a little stumped. Any thoughts as to where the race could be?
> 
> Ok, I've been able to reproduce this with a small module that I wrote
> as a reproducer:

I think I know what's going on.  Looks like a bug in timer code when
timers are queued on a different cpu than before.  Will experiment
with it a bit and report back.

Thanks.

-- 
tejun
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