From: Andrea Arcangeli <aarcange@redhat.com>
Date: Fri, 23 Apr 2010 17:17:39 +0000 (-0400)
Subject: memcg: fix prepare migration
X-Git-Tag: v2.6.34-rc6~54
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=93d5c9be1ddd57d4063ce463c9ac2be1e5ee14f1;p=platform%2Fkernel%2Flinux-3.10.git

memcg: fix prepare migration

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@mxp.nes.nec.co.jp: fix merge issues]
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index f4ede99..6c755de 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2429,11 +2429,11 @@ int mem_cgroup_prepare_migration(struct page *page, struct mem_cgroup **ptr)
 	}
 	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);
 		css_put(&mem->css);
 	}
-	*ptr = mem;
 	return ret;
 }