Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751518Ab1FJEhU (ORCPT ); Fri, 10 Jun 2011 00:37:20 -0400 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:43118 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750733Ab1FJEhR (ORCPT ); Fri, 10 Jun 2011 00:37:17 -0400 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 Date: Fri, 10 Jun 2011 13:30:21 +0900 From: KAMEZAWA Hiroyuki To: KAMEZAWA Hiroyuki Cc: Hugh Dickins , Ying Han , Dave Jones , Linux Kernel , "linux-mm@kvack.org" , Oleg Nesterov , "akpm@linux-foundation.org" Subject: [PATCH] [BUGFIX] update mm->owner even if no next owner. Message-Id: <20110610133021.2eaaf0da.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20110610125551.385ea7ed.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> Organization: FUJITSU Co. 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: 3314 Lines: 91 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 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/