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From: Greg KH on 10 May 2010 19:50
2.6.33-stable review patch. If anyone has any objections, please let us know.

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

From: Andrea Arcangeli <aarcange(a)redhat.com>

commit 93d5c9be1ddd57d4063ce463c9ac2be1e5ee14f1 upstream.

If a signal is pending (task being killed by sigkill)
__mem_cgroup_try_charge will write NULL into &mem, and css_put will oops
on null pointer dereference.

BUG: unable to handle kernel NULL pointer dereference at 0000000000000010
IP: [<ffffffff810fc6cc>] mem_cgroup_prepare_migration+0x7c/0xc0
PGD a5d89067 PUD a5d8a067 PMD 0
Oops: 0000 [#1] SMP
last sysfs file: /sys/devices/platform/microcode/firmware/microcode/loading
CPU 0
Modules linked in: nfs lockd nfs_acl auth_rpcgss sunrpc acpi_cpufreq pcspkr sg [last unloaded: microcode]

Pid: 5299, comm: largepages Tainted: G W 2.6.34-rc3 #3 Penryn1600SLI-110dB/To Be Filled By O.E.M.
RIP: 0010:[<ffffffff810fc6cc>] [<ffffffff810fc6cc>] mem_cgroup_prepare_migration+0x7c/0xc0

[nishimura(a)mxp.nes.nec.co.jp: fix merge issues]
Signed-off-by: Andrea Arcangeli <aarcange(a)redhat.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu(a)jp.fujitsu.com>
Cc: Balbir Singh <balbir(a)in.ibm.com>
Signed-off-by: Daisuke Nishimura <nishimura(a)mxp.nes.nec.co.jp>
Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds(a)linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh(a)suse.de>

---
mm/memcontrol.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2215,12 +2215,12 @@ int mem_cgroup_prepare_migration(struct
}
unlock_page_cgroup(pc);

+ *ptr = mem;
if (mem) {
- ret = __mem_cgroup_try_charge(NULL, GFP_KERNEL, &mem, false,
+ ret = __mem_cgroup_try_charge(NULL, GFP_KERNEL, ptr, false,
page);
css_put(&mem->css);
}
- *ptr = mem;
return ret;
}



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