From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932283AbcHCTbz (ORCPT ); Wed, 3 Aug 2016 15:31:55 -0400 Received: from mail-cys01nam02on0041.outbound.protection.outlook.com ([104.47.37.41]:39008 "EHLO NAM02-CY1-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753938AbcHCTbv (ORCPT ); Wed, 3 Aug 2016 15:31:51 -0400 Authentication-Results: spf=pass (sender IP is 63.163.107.21) smtp.mailfrom=sandisk.com; cmpxchg.org; dkim=none (message not signed) header.d=none;cmpxchg.org; dmarc=bestguesspass action=none header.from=sandisk.com; X-AuditID: ac160c69-5f3ff70000000bcb-0f-57a23c7f4b4e Subject: Re: [PATCH] sched: Avoid that __wait_on_bit_lock() hangs To: Peter Zijlstra References: <20160803181128.GH6879@twins.programming.kicks-ass.net> CC: "mingo@kernel.org" , Andrew Morton , Johannes Weiner , Neil Brown , Michael Shaver , "linux-kernel@vger.kernel.org" , Oleg Nesterov From: Bart Van Assche Message-ID: <11007730-3fa5-139a-8091-655743894ae8@sandisk.com> Date: Wed, 3 Aug 2016 11:56:16 -0700 User-Agent: Mozilla/5.0 (X11; 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Please > clarify. Hello Peter, 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. Please note that the call stack I had mentioned in my e-mail had been reported before. See e.g. * Michael Shaver, Kernel deadlock during mdadm reshape, July 2016 (http://www.spinics.net/lists/raid/msg53056.html). * Bart Van Assche, Kernel hangs in truncate_inode_pages(), August 2012 (https://lkml.org/lkml/2012/8/24/185). Bart.