Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752183Ab1FJFPe (ORCPT ); Fri, 10 Jun 2011 01:15:34 -0400 Received: from TYO201.gate.nec.co.jp ([202.32.8.193]:64092 "EHLO tyo201.gate.nec.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750720Ab1FJFPb (ORCPT ); Fri, 10 Jun 2011 01:15:31 -0400 Date: Fri, 10 Jun 2011 14:06:16 +0900 From: Daisuke Nishimura To: KAMEZAWA Hiroyuki Cc: Hugh Dickins , Ying Han , Dave Jones , Linux Kernel , "linux-mm@kvack.org" , Oleg Nesterov , "akpm@linux-foundation.org" , Daisuke Nishimura Subject: Re: [PATCH] [BUGFIX] update mm->owner even if no next owner. Message-Id: <20110610140616.9f627080.nishimura@mxp.nes.nec.co.jp> In-Reply-To: <20110610133021.2eaaf0da.kamezawa.hiroyu@jp.fujitsu.com> References: <20110609212956.GA2319@redhat.com> <20110610091355.2ce38798.kamezawa.hiroyu@jp.fujitsu.com> <20110610113311.409bb423.kamezawa.hiroyu@jp.fujitsu.com> <20110610121949.622e4629.kamezawa.hiroyu@jp.fujitsu.com> <20110610125551.385ea7ed.kamezawa.hiroyu@jp.fujitsu.com> <20110610133021.2eaaf0da.kamezawa.hiroyu@jp.fujitsu.com> Organization: NEC Soft, Ltd. X-Mailer: Sylpheed 3.1.0 (GTK+ 2.10.14; i686-pc-mingw32) Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4111 Lines: 108 Thank you for your investigation and a patch. I've not been able to replicate this issue on my machine, I think it would be better to push this patch to -stable, if it can fix the issue. Thanks, Daisuke Nishimura. On Fri, 10 Jun 2011 13:30:21 +0900 KAMEZAWA Hiroyuki wrote: > > I think this can be a fix. > maybe good to CC Oleg. > == > From dff52fb35af0cf36486965d19ee79e04b59f1dc4 Mon Sep 17 00:00:00 2001 > From: KAMEZAWA Hiroyuki > Date: Fri, 10 Jun 2011 13:15:14 +0900 > Subject: [PATCH] [BUGFIX] update mm->owner even if no next owner. > > A panic is reported. > > > Call Trace: > > [] mem_cgroup_from_task+0x15/0x17 > > [] __mem_cgroup_try_charge+0x148/0x4b4 > > [] ? need_resched+0x23/0x2d > > [] ? preempt_schedule+0x46/0x4f > > [] mem_cgroup_charge_common+0x9a/0xce > > [] mem_cgroup_newpage_charge+0x5d/0x5f > > [] khugepaged+0x5da/0xfaf > > [] ? __init_waitqueue_head+0x4b/0x4b > > [] ? add_mm_counter.constprop.5+0x13/0x13 > > [] kthread+0xa8/0xb0 > > [] ? sub_preempt_count+0xa1/0xb4 > > [] kernel_thread_helper+0x4/0x10 > > [] ? retint_restore_args+0x13/0x13 > > [] ? __init_kthread_worker+0x5a/0x5a > > The code is. > > return container_of(task_subsys_state(p, mem_cgroup_subsys_id), > > struct mem_cgroup, css); > > > What happens here is accssing a freed task struct "p" from mm->owner. > So, it's doubtful that mm->owner points to freed task struct. > > At thread exit, we need to handle mm->owner. If exitting-thread == mm->owner, > we modify mm->owner to points to other exisiting task. But, we do not update > mm->owner when there are no more threads. But if a kernel thread, like khugepaged, > picks up a mm_struct without updating mm->users, there is a trouble. > > When mm_users shows that the task is the last task belongs to mm. > mm->owner is not updated and remained to point to the task. So, in this case, > mm->owner points to a not exisiting task. This was good because if there > are no thread, no charge happens in old days. But now, we have ksm and > khugepaged. > > rcu_read_lock() used in memcg is of no use because mm->owner can be > freed before we take rcu_read_lock. > Then, mm->owner should be cleared if there are no next owner. > > Reported-by: Hugh Dickins > Reported-by: Dave Jones > Signed-off-by: KAMEZAWA Hiroyuki > --- > kernel/exit.c | 6 ++++-- > 1 files changed, 4 insertions(+), 2 deletions(-) > > diff --git a/kernel/exit.c b/kernel/exit.c > index 20a4064..dbc3736 100644 > --- a/kernel/exit.c > +++ b/kernel/exit.c > @@ -582,8 +582,10 @@ void mm_update_next_owner(struct mm_struct *mm) > struct task_struct *c, *g, *p = current; > > retry: > - if (!mm_need_new_owner(mm, p)) > + if (!mm_need_new_owner(mm, p)) { > + rcu_assign_pointer(mm->owner, NULL); > return; > + } > > read_lock(&tasklist_lock); > /* > @@ -617,7 +619,7 @@ retry: > * most likely racing with swapoff (try_to_unuse()) or /proc or > * ptrace or page migration (get_task_mm()). Mark owner as NULL. > */ > - mm->owner = NULL; > + rcu_assign_pointer(mm->owner, NULL); > return; > > assign_new_owner: > -- > 1.7.4.1 > > > -- > 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/ . > Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ > Don't email: email@kvack.org -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/