linux-kernel - Re: [RFC][PATCH] fix move/migrate

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Message-ID: <m2zkc9pexf.fsf@firstfloor.org>
Date:	Thu, 23 Feb 2012 10:45:00 -0800
From:	Andi Kleen <andi@...stfloor.org>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	cl@...ux.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC][PATCH] fix move/migrate_pages() race on task struct

Dave Hansen <dave@...ux.vnet.ibm.com> writes:

> sys_move_pages() and sys_migrate_pages() are a pretty nice copy
> and paste job of each other.  They both take a pid, find the task
> struct, and then grab a ref on the mm.  They both also do an
> rcu_read_unlock() after they've taken the mm and then proceed to
> access 'task'.  I think this is a bug in both cases.

Can we share code?


>
> This patch takes the pid-to-task code along with the credential
> and security checks in sys_move_pages() and sys_migrate_pages()
> and consolidates them.  It now takes a task reference in
> the new function and requires the caller to drop it.  I
> believe this resolves the race.

Looks good to me.

Reviewed-by: Andi Kleen <ak@...ux.intel.com>

BTW looks like we really need a better stress test for these
syscalls.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only
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