linux-kernel - Re: [PATCH] mm/mempolicy.c: do not put mempolicy before using its nodemask

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Message-ID: <20170118170444.s4z5jqn57fqbnvnf@black.fi.intel.com>
Date:   Wed, 18 Jan 2017 20:04:45 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.vnet.ibm.com>,
        David Rientjes <rientjes@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH] mm/mempolicy.c: do not put mempolicy before using its
 nodemask

On Wed, Jan 18, 2017 at 03:11:24PM +0100, Vlastimil Babka wrote:
> Since commit be97a41b291e ("mm/mempolicy.c: merge alloc_hugepage_vma to
> alloc_pages_vma") alloc_pages_vma() can potentially free a mempolicy by
> mpol_cond_put() before accessing the embedded nodemask by
> __alloc_pages_nodemask(). The commit log says it's so "we can use a single
> exit path within the function" but that's clearly wrong. We can still do that
> when doing mpol_cond_put() after the allocation attempt.
> 
> Make sure the mempolicy is not freed prematurely, otherwise
> __alloc_pages_nodemask() can end up using a bogus nodemask, which could lead
> e.g. to premature OOM.
> 
> Fixes: be97a41b291e ("mm/mempolicy.c: merge alloc_hugepage_vma to alloc_pages_vma")
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> Cc: stable@...r.kernel.org
> Cc: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: Andrea Arcangeli <aarcange@...hat.com>

Looks good to me.

Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

-- 
 Kirill A. Shutemov