From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932901AbcHCVvj (ORCPT ); Wed, 3 Aug 2016 17:51:39 -0400 Received: from mail-co1nam03on0044.outbound.protection.outlook.com ([104.47.40.44]:30991 "EHLO NAM03-CO1-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S932176AbcHCVvg (ORCPT ); Wed, 3 Aug 2016 17:51:36 -0400 X-Greylist: delayed 110139 seconds by postgrey-1.27 at vger.kernel.org; Wed, 03 Aug 2016 17:51:36 EDT Authentication-Results: spf=pass (sender IP is 63.163.107.225) smtp.mailfrom=sandisk.com; gmail.com; dkim=none (message not signed) header.d=none;gmail.com; dmarc=bestguesspass action=none header.from=sandisk.com; X-AuditID: ac160c71-eb3ff70000000e72-c7-57a265ded5f0 Subject: Re: [PATCH] sched: Avoid that __wait_on_bit_lock() hangs To: Oleg Nesterov References: <20160803181128.GH6879@twins.programming.kicks-ass.net> <11007730-3fa5-139a-8091-655743894ae8@sandisk.com> <20160803213006.GA11712@redhat.com> CC: Peter Zijlstra , "mingo@kernel.org" , Andrew Morton , "Johannes Weiner" , Neil Brown , Michael Shaver , "linux-kernel@vger.kernel.org" From: Bart Van Assche Message-ID: <17b65ff9-215f-ab74-9f5f-15dbd308d054@sandisk.com> Date: Wed, 3 Aug 2016 14:51:23 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2 MIME-Version: 1.0 In-Reply-To: <20160803213006.GA11712@redhat.com> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFprCIsWRmVeSWpSXmKPExsWyRoxnke6j1EXhBhOPC1vMWb+GzWL1Jl+L NZMesllc3jUHyPt3itFi7/wGFout+1sZLY73HmBy4PA4/OY9s8fOWXfZPTav0PLYtKqTzePE jN8sHu/3XWXz2Hy62uPzJrkAjigum5TUnMyy1CJ9uwSujKt/7zIWHBWpuLlpAnsD4zzBLkYO DgkBE4lre827GDk5hASWMkl8/5LYxcgFZG9nlFh8bgYTSAKk5vCnmywQiaWMEtcXbQJLCAs4 Smzd/5kZxBYRUJb4c28BM0TRZUaJKX+nsoM4zAIrmSSe3Z/IClLFJmAk8e39TBYQm1fATmLX 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1;CY1PR02MB1304;20:BAGdfp8iC0UmTQ3zBSqFMBdxrdt3wppzLv8j8bQS9wjPxm1n1N+Mg061GLv9Q8kV64r679adyPcOG38zTnJhabNpOMAT34p1bb1ny6SIwy+1HirmK9g8cf5VIS9EmyROGlnl+mbnkak1CyFZJYvORTomYcweWahow68IhVvft6wqcLRSLyzpadXi6t0MJrmtSvKoKAMuBOB0Hgh9WWm7JZAVQ0jq8o02Ba8wDJQhyJLhxB9fP+8YXmwwlp0BbX8m X-OriginatorOrg: sandisk.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 03 Aug 2016 21:51:31.7202 (UTC) X-MS-Exchange-CrossTenant-Id: fcd9ea9c-ae8c-460c-ab3c-3db42d7ac64d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=fcd9ea9c-ae8c-460c-ab3c-3db42d7ac64d;Ip=[63.163.107.225];Helo=[milsmgep14.sandisk.com] X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY1PR02MB1304 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/03/2016 02:30 PM, Oleg Nesterov wrote: > On 08/03, Bart Van Assche wrote: >> try_to_wake_up() locks task_struct.pi_lock but abort_exclusive_wait() not. >> My assumption is that the following sequence of events leads to the lockup >> that I had mentioned in the description of my patch: >> * try_to_wake_up() is called for the task that will execute >> abort_exclusive_wait(). >> * After try_to_wake_up() has checked task_struct.state and before >> autoremove_wake_function() has tried to remove the task from the wait >> queue, abort_exclusive_wait() is executed for the same task. > > But we do not care if we race with another try_to_wake_up(), or even with > another exclusive wake_up_nr(wq)/whatever unless wq is the same. > > And if this wq is the same, then wake_up_nr() will do try_to_wake_up/autoremove > either before or after abort_exclusive_wait(), wake_up_nr() takes the same > wq->lock. > > And this means that abort_exclusive_wait() can't be called "After try_to_wake_up()" > and "before autoremove_wake_function()". Hello Oleg, It is possible that my analysis is wrong. But what I see is that my patch makes the lockup disappear. However, what I had not expected is that I ran into the following (probably caused by the patch at the start of this thread): WARNING: CPU: 1 PID: 26023 at lib/list_debug.c:33 __list_add+0x89/0xb0 list_add corruption. prev->next should be next (ffff88047ff4b0c8), but was ffff8803cbc037e0. (prev=ffff8803c863bd80). Call Trace: [] dump_stack+0x68/0xa1 [] __warn+0xc6/0xe0 [] warn_slowpath_fmt+0x4a/0x50 [] __list_add+0x89/0xb0 [] prepare_to_wait_exclusive+0x79/0x80 [] __wait_on_bit_lock+0x2f/0xa0 [] __lock_page+0xb9/0xc0 [] truncate_inode_pages_range+0x3e0/0x760 [] truncate_inode_pages+0x10/0x20 [ ... ] So I started testing the patch below that should fix the same hang but without triggering any wait list corruption. Bart. diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c index f15d6b6..4e3f651 100644 --- a/kernel/sched/wait.c +++ b/kernel/sched/wait.c @@ -282,7 +282,7 @@ void abort_exclusive_wait(wait_queue_head_t *q, wait_queue_t *wait, spin_lock_irqsave(&q->lock, flags); if (!list_empty(&wait->task_list)) list_del_init(&wait->task_list); - else if (waitqueue_active(q)) + if (waitqueue_active(q)) __wake_up_locked_key(q, mode, key); spin_unlock_irqrestore(&q->lock, flags); }