Re: [PATCH v3 7/9] mm/page_owner: avoid null pointer dereference
From: Vlastimil Babka <hidden>
Date: 2016-06-17 13:32:32
Also in:
lkml
On 06/17/2016 09:57 AM, js1304@gmail.com wrote:
From: Sudip Mukherjee <sudipm.mukherjee@gmail.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@codethink.co.uk> Signed-off-by: Joonsoo Kim <redacted>
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 <redacted> Fixes: f86e4271978b ("mm: check the return value of lookup_page_ext for all call sites")
quoted hunk ↗ jump to hunk
--- 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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