David Rientjes 668f9abbd4 mm: close PageTail race ... Commit bf6bddf192 ("mm: introduce compaction and migration for ballooned pages") introduces page_count(page) into memory compaction which dereferences page->first_page if PageTail(page). This results in a very rare NULL pointer dereference on the aforementioned page_count(page). Indeed, anything that does compound_head(), including page_count() is susceptible to racing with prep_compound_page() and seeing a NULL or dangling page->first_page pointer. This patch uses Andrea's implementation of compound_trans_head() that deals with such a race and makes it the default compound_head() implementation. This includes a read memory barrier that ensures that if PageTail(head) is true that we return a head page that is neither NULL nor dangling. The patch then adds a store memory barrier to prep_compound_page() to ensure page->first_page is set. This is the safest way to ensure we see the head page that we are expecting, PageTail(page) is already in the unlikely() path and the memory barriers are unfortunately required. Hugetlbfs is the exception, we don't enforce a store memory barrier during init since no race is possible. Signed-off-by: David Rientjes <rientjes@google.com> Cc: Holger Kiehl <Holger.Kiehl@dwd.de> Cc: Christoph Lameter <cl@linux.com> Cc: Rafael Aquini <aquini@redhat.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Michal Hocko <mhocko@suse.cz> Cc: Mel Gorman <mgorman@suse.de> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Rik van Riel <riel@redhat.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>		2014-03-04 07:55:47 -08:00
..
aoe.h	aoe: Convert to immutable biovecs	2013-11-23 22:33:52 -08:00
aoeblk.c	aoe: do not BUG if memory pressure prevented debugfs file creation	2013-09-11 15:59:28 -07:00
aoechr.c	aoe: replace kmalloc and then memcpy with kmemdup	2013-04-30 17:04:08 -07:00
aoecmd.c	mm: close PageTail race	2014-03-04 07:55:47 -08:00
aoedev.c	aoe: remove custom implementation of kbasename()	2013-09-11 15:59:26 -07:00
aoemain.c	aoe: whitespace cleanup	2012-12-17 17:15:24 -08:00
aoenet.c	aoe: update copyright date	2013-07-03 16:08:05 -07:00
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