[010/117] memcg: fix prepare migration

[Greg KH]

2.6.33-stable review patch.  If anyone has any objections, please let us know.

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

From: Andrea Arcangeli <aarcange@xxxxxxxxxx>

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@xxxxxxxxxxxxxxxxx: fix merge issues]
Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Cc: Balbir Singh <balbir@xxxxxxxxxx>
Signed-off-by: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 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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