linux-kernel - [ 65/82] mm: bugfix: set current->reclaim_state to NULL while returning from kswapd()

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Message-Id: <20121114053942.803321723@decadent.org.uk>
Date:	Wed, 14 Nov 2012 05:40:38 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Takamori Yamaguchi <takamori.yamaguchi@...sony.com>,
	Aaditya Kumar <aaditya.kumar@...sony.com>,
	David Rientjes <rientjes@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [ 65/82] mm: bugfix: set current->reclaim_state to NULL while returning from
 kswapd()

3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Takamori Yamaguchi <takamori.yamaguchi@...sony.com>

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@...sony.com>
Signed-off-by: Aaditya Kumar <aaditya.kumar@...sony.com>
Acked-by: David Rientjes <rientjes@...gle.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 mm/vmscan.c |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2624edc..8b055e9 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3017,6 +3017,8 @@ static int kswapd(void *p)
 						&balanced_classzone_idx);
 		}
 	}
+
+	current->reclaim_state = NULL;
 	return 0;
 }
 


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