linux-kernel - Re: [PATCH 1/2] mm/page_alloc: avoid potential NULL pointer dereference

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Message-ID: <20190423143540.GQ18914@techsingularity.net>
Date:   Tue, 23 Apr 2019 15:35:40 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mm/page_alloc: avoid potential NULL pointer
 dereference

On Tue, Apr 23, 2019 at 03:08:05PM +0300, Andrey Ryabinin wrote:
> ac.preferred_zoneref->zone passed to alloc_flags_nofragment() can be NULL.
> 'zone' pointer unconditionally derefernced in alloc_flags_nofragment().
> Bail out on NULL zone to avoid potential crash.
> Currently we don't see any crashes only because alloc_flags_nofragment()
> has another bug which allows compiler to optimize away all accesses to
> 'zone'.
> 
> Fixes: 6bb154504f8b ("mm, page_alloc: spread allocations across zones before introducing fragmentation")
> Signed-off-by: Andrey Ryabinin <aryabinin@...tuozzo.com>

Acked-by: Mel Gorman <mgorman@...hsingularity.net>

-- 
Mel Gorman
SUSE Labs