Re: [BUGFIX][PATCH -mm] fix bad call of memcg_oom_recover at cancel move.

[Balbir Singh <balbir@linux.vnet.ibm.com>]

* KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2010-06-17 17:20:34]:

> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> 
> When cgroup_cancel_attach() is called via cgroup_attach_task(),
> mem_cgroup_clear_mc() can be called even when any migration
> was done. In such case, mc.to and mc.from is NULL.
> 
> But, memcg-clean-up-waiting-move-acct-v2.patch
> doesn't handle this correctly and pass NULL to memcg_oom_recover.
> fix it.
> 
> BUG: unable to handle kernel paging request at 000000000000114c
> IP: [<ffffffff81153bb9>] memcg_oom_recover+0x9/0x30
> PGD 61ce4b067 PUD 613ea0067 PMD 0
> Oops: 0000 [#1] SMP
> <snip>
> Call Trace:
>  [<ffffffff81155359>] mem_cgroup_clear_mc+0x119/0x1c0
>  [<ffffffff811554de>] mem_cgroup_cancel_attach+0xe/0x10
>  [<ffffffff810b619c>] cgroup_attach_task+0x26c/0x2c0
>  [<ffffffff810b6257>] cgroup_tasks_write+0x67/0x1c0
>  [<ffffffff81121555>] ? might_fault+0xa5/0xb0
>  [<ffffffff8112150c>] ? might_fault+0x5c/0xb0
>  [<ffffffff810b40a2>] cgroup_file_write+0x2d2/0x330
>  [<ffffffff81093aa2>] ? print_lock_contention_bug+0x22/0xf0
>  [<ffffffff81259fef>] ? security_file_permission+0x1f/0x80
>  [<ffffffff8115d998>] vfs_write+0xc8/0x190
>  [<ffffffff8115e3a1>] sys_write+0x51/0x90
>  [<ffffffff8100b072>] system_call_fastpath+0x16/0x1b
> Code: 20 48 39 43 20 41 bc f0 ff ff ff 75 c7 45 88 ae 48 11 00 00 45 31 e4 eb bb 66 0f 1f 84 00 00 00 00 00 55 48 89 e5 0f 1f 44 00 00 <8b> 87 4c 11 00 00 85 c0 75 05 c9 c3 0f 1f 00 48 89 f9 31 d2 be
> RIP  [<ffffffff81153bb9>] memcg_oom_recover+0x9/0x30
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> ---
>  mm/memcontrol.c |    6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> Index: mmotm-2.6.35-0611/mm/memcontrol.c
> ===================================================================
> --- mmotm-2.6.35-0611.orig/mm/memcontrol.c
> +++ mmotm-2.6.35-0611/mm/memcontrol.c
> @@ -4485,8 +4485,10 @@ static void mem_cgroup_clear_mc(void)
>  	mc.to = NULL;
>  	mc.moving_task = NULL;
>  	spin_unlock(&mc.lock);
> -	memcg_oom_recover(from);
> -	memcg_oom_recover(to);
> +	if (from)
> +		memcg_oom_recover(from);
> +	if (to)
> +		memcg_oom_recover(to);
>  	wake_up_all(&mc.waitq);

May I recommend the following change instead


Don't crash on a null memcg being passed, check if memcg
is NULL and handle the condition gracefully

Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
---
 mm/memcontrol.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c6ece0a..d71c488 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1370,7 +1370,7 @@ static void memcg_wakeup_oom(struct mem_cgroup *mem)
 
 static void memcg_oom_recover(struct mem_cgroup *mem)
 {
-	if (mem->oom_kill_disable && atomic_read(&mem->oom_lock))
+	if (mem && mem->oom_kill_disable && atomic_read(&mem->oom_lock))
 		memcg_wakeup_oom(mem);
 }
 
-- 
1.7.0.1


-- 
	Three Cheers,
	Balbir

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