linux-kernel - Re: [PATCH 2/2] stop_machine: dequeue work before signal completion

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Message-ID: <20130212173812.GG7348@htj.dyndns.org>
Date:	Tue, 12 Feb 2013 09:38:12 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Hillf Danton <dhillf@...il.com>
Cc:	Namhyung Kim <namhyung@...nel.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Stable <stable@...r.kernel.org>
Subject: Re: [PATCH 2/2] stop_machine: dequeue work before signal completion

On Sun, Feb 10, 2013 at 01:26:11PM +0800, Hillf Danton wrote:
> When a CPU is finally put down in either CPU_UP_CANCELLED or
> CPU_POST_DEAD, cpu_stop_cpu_callback() signals immediate completion on
> all cpu_stop_works still queued on the dead CPU; unfortunately, this
> code is buggy in that it doesn't remove the canceled work items off
> the stopper->works leaving it corrupted, which will trigger BUG_ON()
> during CPU_UP_PREPARE if the CPU is brought back online.
> 
> This bug isn't easily triggered because CPU_DOWN has to race against
> cpu_stop calls and most, if not all, cpu stop users pin target CPUs.
> 
> Fix it by popping each work item off stopper->works.
> 
> Thanks Tejun for sharing commit message, again.
> 
> Signed-off-by: Hillf Danton <dhillf@...il.com>
> Reviewed-by: Namhyung Kim <namhyung@...nel.org>
> Cc: stable@...r.kernel.org

Acked-by: Tejun Heo <tj@...nel.org>

Andrew, this one too.

Thank you!

-- 
tejun
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