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Message-ID: <09cfe295-87d0-16d9-36ed-458378b3bd05@suse.cz>
Date: Fri, 17 Jun 2016 15:32:20 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: js1304@...il.com, Andrew Morton <akpm@...ux-foundation.org>
Cc: mgorman@...hsingularity.net, Minchan Kim <minchan@...nel.org>,
Alexander Potapenko <glider@...gle.com>,
Hugh Dickins <hughd@...gle.com>,
Michal Hocko <mhocko@...nel.org>, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, Sasha Levin <sasha.levin@...cle.com>,
Sudip Mukherjee <sudipm.mukherjee@...il.com>,
Sudip Mukherjee <sudip.mukherjee@...ethink.co.uk>,
Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v3 7/9] mm/page_owner: avoid null pointer dereference
On 06/17/2016 09:57 AM, js1304@...il.com wrote:
> From: Sudip Mukherjee <sudipm.mukherjee@...il.com>
>
> We have dereferenced page_ext before checking it. Lets check it first
> and then used it.
>
> Link: http://lkml.kernel.org/r/1465249059-7883-1-git-send-email-sudipm.mukherjee@gmail.com
> Signed-off-by: Sudip Mukherjee <sudip.mukherjee@...ethink.co.uk>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
Hmm, this is already in mmotm as
http://www.ozlabs.org/~akpm/mmotm/broken-out/mm-page_owner-use-stackdepot-to-store-stacktrace-fix.patch
But imho it's fixing a problem not related to your patch, but something that the
commit f86e4271978b missed. So it should separately go to 4.7 ASAP.
Acked-by: Vlastimil Babka <vbabka@...e.cz>
Fixes: f86e4271978b ("mm: check the return value of lookup_page_ext for all call
sites")
> ---
> mm/page_owner.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index dc92241..ec6dc18 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -295,13 +295,15 @@ void __dump_page_owner(struct page *page)
> .skip = 0
> };
> depot_stack_handle_t handle;
> - gfp_t gfp_mask = page_ext->gfp_mask;
> - int mt = gfpflags_to_migratetype(gfp_mask);
> + gfp_t gfp_mask;
> + int mt;
>
> if (unlikely(!page_ext)) {
> pr_alert("There is not page extension available.\n");
> return;
> }
> + gfp_mask = page_ext->gfp_mask;
> + mt = gfpflags_to_migratetype(gfp_mask);
>
> if (!test_bit(PAGE_EXT_OWNER, &page_ext->flags)) {
> pr_alert("page_owner info is not active (free page?)\n");
>
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