* KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> [2010-06-17 17:20:34]:
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxx>
> ---
> 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@xxxxxxxxxxxxxxxxxx>
---
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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