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
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acpi	Merge branches 'acpi-processor', 'acpi-hotplug', 'acpi-init', 'acpi-pm' and 'acpica'	2014-01-29 11:47:18 +01:00
asm-generic	mm: Use ptep/pmdp_set_numa() for updating _PAGE_NUMA bit	2014-02-17 11:19:36 +11:00
clocksource	…
crypto	…
drm	Merge tag 'ttm-fixes-3.14-2014-02-18' of git://people.freedesktop.org/~thomash/linux into drm-fixes	2014-02-19 08:21:26 +10:00
dt-bindings	Merge branch 'next' of git://git.kernel.org/pub/scm/linux/kernel/git/benh/powerpc	2014-01-30 17:07:18 -08:00
keys	…
kvm	…
linux	mm: close PageTail race	2014-03-04 07:55:47 -08:00
math-emu	…
media	…
memory	…
misc	…
net	net: sctp: Fix a_rwnd/rwnd management to reflect real state of the receiver's buffer	2014-02-17 00:16:56 -05:00
pcmcia	…
ras	…
rdma	IB: Report using RoCE IP based gids in port caps	2014-02-13 14:46:03 -08:00
rxrpc	…
scsi	Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/nab/target-pending	2014-01-31 15:31:23 -08:00
sound	ASoC: dapm: Add locking to snd_soc_dapm_xxxx_pin functions	2014-02-20 18:40:07 +09:00
target	target: Simplify command completion by removing CMD_T_FAILED flag	2014-02-12 15:14:30 -08:00
trace	Revert "writeback: do not sync data dirtied after sync start"	2014-02-22 02:02:28 +01:00
uapi	asm-generic: add sched_setattr/sched_getattr syscalls	2014-02-24 11:55:20 +00:00
video	…
xen	Merge branch 'for-linus' of git://git.kernel.dk/linux-block	2014-02-14 10:45:18 -08:00
Kbuild	…