From: Michal Hocko <mhocko@kernel.org>
To: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Tejun Heo <tj@kernel.org>, LKML <linux-kernel@vger.kernel.org>
Subject: Re: mod_delayed_work() explosion due to 874bbfe6
Date: Wed, 3 Feb 2016 15:37:00 +0100 [thread overview]
Message-ID: <20160203143700.GD6762@dhcp22.suse.cz> (raw)
In-Reply-To: <1454424264.11183.46.camel@gmail.com>
On Tue 02-02-16 15:44:24, Mike Galbraith wrote:
> Hi Tejun,
>
> I'm looking at a crash analysis that fingers 874bbfe6 as being the
> culprit. (I didn't do the analysis, but it appears to be correct)
>
> Scenario: CPU168 calls mod_delayed_work(), is taken offline before the
> timer expires. Due to 874bbfe6, dwork->cpu is the now offline CPU168
> vs the previous WORK_CPU_UNBOUND, timer fires on CPU131, it tries to
> __queue_work() with cpu == the now offline CPU168, gets to...
>
> } else
> pwq = unbound_pwq_by_node(wq, cpu_to_node(cpu));
>
> ... and goes boom.
>
> <snippet>
> crash> p numa_node | grep 168
> [168]: ffff8c03fdf0e328
> crash> rd ffff8c03fdf0e328
> ffff8c03fdf0e328: 00000000ffffffff ........
>
> Thus, pwq becomes 000000000. Then, as the result of reference to
> pwq->pool, NULL reference occurs at (*PANIC).
> </snippet>
>
> What if anything is supposed to prevent this?
AFAICS [1] nothing...
---
[1] http://lkml.kernel.org/r/20160203122855.GB6762@dhcp22.suse.cz
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2016-02-03 14:37 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-02 14:44 mod_delayed_work() explosion due to 874bbfe6 Mike Galbraith
2016-02-03 14:37 ` Michal Hocko [this message]
2016-02-03 16:32 ` Tejun Heo
2016-02-03 18:54 ` [PATCH wq/for-4.5-fixes] workqueue: handle NUMA_NO_NODE for unbound pool_workqueue lookup Tejun Heo
2016-02-03 18:55 ` Tejun Heo
2016-02-04 3:15 ` Mike Galbraith
2016-02-03 19:12 ` Thomas Gleixner
2016-02-03 19:28 ` Tejun Heo
2016-02-04 2:12 ` Mike Galbraith
2016-02-04 8:40 ` Michal Hocko
2016-02-10 15:55 ` Tejun Heo
2016-02-15 17:33 ` Michal Hocko
2016-02-15 18:21 ` Tejun Heo
2016-02-15 20:54 ` Michal Hocko
2016-02-15 21:02 ` Tejun Heo
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