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Commit 8285027f authored by Sudip Mukherjee's avatar Sudip Mukherjee Committed by Linus Torvalds
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mm/page_owner: avoid null pointer dereference 

We have dereferenced page_ext before checking it.  Lets check it first
and then used it.

Fixes: f86e4271 ("mm: check the return value of lookup_page_ext for all call sites")
Link: http://lkml.kernel.org/r/1465249059-7883-1-git-send-email-sudipm.mukherjee@gmail.com


Signed-off-by: default avatarSudip Mukherjee <sudip.mukherjee@codethink.co.uk>
Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 7c5b7239

mm/page_owner.c

+4 −2
Original line number Diff line number Diff line
@@ -207,13 +207,15 @@ void __dump_page_owner(struct page *page) 
		.nr_entries = page_ext->nr_entries,

		.entries = &page_ext->trace_entries[0],

	};

	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");