linux-kernel - Re: [PATCH v4] slab/mempolicy: always use local policy from interrupt context

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Message-ID: <alpine.DEB.2.00.1205311340170.2764@chino.kir.corp.google.com>
Date:	Thu, 31 May 2012 13:41:29 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	David Mackey <tdmackey@...tter.com>
cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Andi Kleen <ak@...ux.intel.com>, penberg@...nel.org,
	cl@...ux.com
Subject: Re: [PATCH v4] slab/mempolicy: always use local policy from interrupt
 context

On Wed, 30 May 2012, David Mackey wrote:

> From: Andi Kleen <ak@...ux.intel.com>
> 
> slab_node() could access current->mempolicy from interrupt context.
> However there's a race condition during exit where the mempolicy
> is first freed and then the pointer zeroed.
> 
> Using this from interrupts seems bogus anyways. The interrupt
> will interrupt a random process and therefore get a random
> mempolicy. Many times, this will be idle's, which noone can change.
> 
> Just disable this here and always use local for slab
> from interrupts. I also cleaned up the callers of slab_node a bit
> which always passed the same argument.
> 
> I believe the original mempolicy code did that in fact,
> so it's likely a regression.
> 
> v2: send version with correct logic
> v3: simplify. fix typo.
> Reported-by: Arun Sharma <asharma@...com>
> Cc: penberg@...nel.org
> Cc: cl@...ux.com
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> [tdmackey@...tter.com: Rework patch logic and avoid dereference of current 
> task if in interrupt context.]
> Signed-off-by: David Mackey <tdmackey@...tter.com>

Acked-by: David Rientjes <rientjes@...gle.com>

Thanks for following up on this.
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