linux-kernel - Re: [PATCH 1/3 v2] call_function_many: fix list delete vs add race

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Date:	Wed, 02 Feb 2011 07:22:01 +0100
From:	Mike Galbraith <efault@....de>
To:	Milton Miller <miltonm@....com>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	akpm@...ux-foundation.org, Anton Blanchard <anton@...ba.org>,
	xiaoguangrong@...fujitsu.com, mingo@...e.hu, jaxboe@...ionio.com,
	npiggin@...il.com, JBeulich@...ell.com, rusty@...tcorp.com.au,
	torvalds@...ux-foundation.org, benh@...nel.crashing.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3 v2] call_function_many: fix list delete vs add race

On Tue, 2011-02-01 at 14:00 -0800, Milton Miller wrote:
> On Tue, 1 Feb 2011 about 14:00:26 -0800, "Paul E. McKenney" wrote:

> > Starting with smp_call_function_many():
> > 
> > o	The check for refs is redundant:
> > 
> > 		/* some callers might race with other cpus changing the mask */
> > 		if (unlikely(!refs)) {
> > 			csd_unlock(&data->csd);
> > 			return;
> > 		}
> > 
> > 	The memory barriers and atomic functions in
> > 	generic_smp_call_function_interrupt() prevent the callback from
> > 	being reused before the cpumask bits have all been cleared, right?
> 
> The issue is not the cpumask in the csd, but the mask passed in from the
> caller.  If other cpus clear the mask between the cpumask_first and and
> cpumask_next above (where we established there were at least two cpus not
> ourself) and the cpumask_copy, then this can happen.  Both Mike Galbraith
> and Jan Beulich saw this in practice (Mikes case was mm_cpumask(mm)).

Mine (and Jan's) is a flavor of one hit and fixed via copy in ia64.

http://git2.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=75c1c91cb92806f960fcd6e53d2a0c21f343081c


	-Mike

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