From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from d23relay03.au.ibm.com (d23relay03.au.ibm.com [202.81.18.234]) by e23smtp04.au.ibm.com (8.13.1/8.13.1) with ESMTP id m3E7vLEr004493 for ; Mon, 14 Apr 2008 17:57:21 +1000 Received: from d23av02.au.ibm.com (d23av02.au.ibm.com [9.190.235.138]) by d23relay03.au.ibm.com (8.13.8/8.13.8/NCO v8.7) with ESMTP id m3E7vpNX3928278 for ; Mon, 14 Apr 2008 17:57:52 +1000 Received: from d23av02.au.ibm.com (loopback [127.0.0.1]) by d23av02.au.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id m3E7vrSK017873 for ; Mon, 14 Apr 2008 17:57:54 +1000 Message-ID: <48030DFF.9070407@linux.vnet.ibm.com> Date: Mon, 14 Apr 2008 13:25:43 +0530 From: Balbir Singh Reply-To: balbir@linux.vnet.ibm.com MIME-Version: 1.0 Subject: Re: [PATCH] memcg: fix oops in oom handling References: <4802FF10.6030905@cn.fujitsu.com> In-Reply-To: <4802FF10.6030905@cn.fujitsu.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Li Zefan Cc: Andrew Morton , KAMEZAWA Hiroyuki , Pavel Emelianov , Paul Menage , LKML , "linux-mm@kvack.org" List-ID: Li Zefan wrote: > When I used a test program to fork mass processes and immediately > move them to a cgroup where the memory limit is low enough to > trigger oom kill, I got oops: > > BUG: unable to handle kernel NULL pointer dereference at 0000000000000808 > IP: [] _spin_lock_irqsave+0x8/0x18 > PGD 4c95f067 PUD 4406c067 PMD 0 > Oops: 0002 [1] SMP > CPU 2 > Modules linked in: > > Pid: 11973, comm: a.out Not tainted 2.6.25-rc7 #5 > RIP: 0010:[] [] _spin_lock_irqsave+0x8/0x18 > RSP: 0018:ffff8100448c7c30 EFLAGS: 00010002 > RAX: 0000000000000202 RBX: 0000000000000009 RCX: 000000000001c9f3 > RDX: 0000000000000100 RSI: 0000000000000001 RDI: 0000000000000808 > RBP: ffff81007e444080 R08: 0000000000000000 R09: ffff8100448c7900 > R10: ffff81000105f480 R11: 00000100ffffffff R12: ffff810067c84140 > R13: 0000000000000001 R14: ffff8100441d0018 R15: ffff81007da56200 > FS: 00007f70eb1856f0(0000) GS:ffff81007fbad3c0(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b > CR2: 0000000000000808 CR3: 000000004498a000 CR4: 00000000000006e0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 > Process a.out (pid: 11973, threadinfo ffff8100448c6000, task ffff81007da533e0) > Stack: ffffffff8023ef5a 00000000000000d0 ffffffff80548dc0 00000000000000d0 > ffff810067c84140 ffff81007e444080 ffffffff8026cef9 00000000000000d0 > ffff8100441d0000 00000000000000d0 ffff8100441d0000 ffff8100505445c0 > Call Trace: > [] ? force_sig_info+0x25/0xb9 > [] ? oom_kill_task+0x77/0xe2 > [] ? mem_cgroup_out_of_memory+0x55/0x67 > [] ? mem_cgroup_charge_common+0xec/0x202 > [] ? handle_mm_fault+0x24e/0x77f > [] ? default_wake_function+0x0/0xe > [] ? get_user_pages+0x2ce/0x3af > [] ? mem_cgroup_charge_common+0x2d/0x202 > [] ? make_pages_present+0x8e/0xa4 > [] ? mmap_region+0x373/0x429 > [] ? do_mmap_pgoff+0x2ff/0x364 > [] ? sys_mmap+0xe5/0x111 > [] ? tracesys+0xdc/0xe1 > > Code: 00 00 01 48 8b 3c 24 e9 46 d4 dd ff f0 ff 07 48 8b 3c 24 e9 3a d4 dd ff fe 07 48 8b 3c 24 e9 2f d4 dd ff 9c 58 fa ba 00 01 00 00 66 0f c1 17 38 f2 74 06 f3 90 8a 17 eb f6 c3 fa b8 00 01 00 > RIP [] _spin_lock_irqsave+0x8/0x18 > RSP > CR2: 0000000000000808 > ---[ end trace c3702fa668021ea4 ]--- > > It's reproducable in a x86_64 box, but doesn't happen in x86_32. > > This is because tsk->sighand is not guarded by RCU, so we have to > hold tasklist_lock, just as what out_of_memory() does. > > Signed-off-by: Li Zefan > --- > mm/oom_kill.c | 4 ++-- > 1 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > index f255eda..beb592f 100644 > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > @@ -423,7 +423,7 @@ void mem_cgroup_out_of_memory(struct mem_cgroup *mem, gfp_t gfp_mask) > struct task_struct *p; > > cgroup_lock(); > - rcu_read_lock(); > + read_lock(&tasklist_lock); > retry: > p = select_bad_process(&points, mem); > if (PTR_ERR(p) == -1UL) > @@ -436,7 +436,7 @@ retry: > "Memory cgroup out of memory")) > goto retry; > out: > - rcu_read_unlock(); > + read_unlock(&tasklist_lock); > cgroup_unlock(); > } > #endif > -- 1.5.4.rc3 This looks sane to me Acked-by: Balbir Singh -- Warm Regards, Balbir Singh Linux Technology Center IBM, ISTL -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org