[v2.6.34-stable 102/213] mm: bugfix: set current->reclaim_state to NULL while returning from kswapd()

[Paul Gortmaker]

From: Takamori Yamaguchi <takamori.yamaguchi@xxxxxxxxxxx>

                   -------------------
    This is a commit scheduled for the next v2.6.34 longterm release.
    http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git
    If you see a problem with using this for longterm, please comment.
                   -------------------

commit b0a8cc58e6b9aaae3045752059e5e6260c0b94bc upstream.

In kswapd(), set current->reclaim_state to NULL before returning, as
current->reclaim_state holds reference to variable on kswapd()'s stack.

In rare cases, while returning from kswapd() during memory offlining,
__free_slab() and freepages() can access the dangling pointer of
current->reclaim_state.

Signed-off-by: Takamori Yamaguchi <takamori.yamaguchi@xxxxxxxxxxx>
Signed-off-by: Aaditya Kumar <aaditya.kumar@xxxxxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
---
 mm/vmscan.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 5c4620600333..365a899bcae0 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2341,6 +2341,8 @@ static int kswapd(void *p)
 		if (!ret)
 			balance_pgdat(pgdat, order);
 	}
+
+	current->reclaim_state = NULL;
 	return 0;
 }
 
-- 
1.8.5.2

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