linux-kernel - Re: mpol_to

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Message-ID: <alpine.DEB.2.00.1210081344440.18768@chino.kir.corp.google.com>
Date:	Mon, 8 Oct 2012 13:46:38 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	bhutchings@...arflare.com, linux-mm@...ck.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: mpol_to_str revisited.

On Mon, 8 Oct 2012, Dave Jones wrote:

> If pol->mode was poisoned, that smells like we have a race where policy is getting freed
> while another process is reading it.
> 
> Am I missing something, or is there no locking around that at all ?
> 

The only thing that is held during the read() is a reference to the 
task_struct so it doesn't disappear from under us.  The protection needed 
for a task's mempolicy, however, is task_lock() and that is not held.
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