Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755467AbbHYKSn (ORCPT ); Tue, 25 Aug 2015 06:18:43 -0400 Received: from blu004-omc1s19.hotmail.com ([65.55.116.30]:61934 "EHLO BLU004-OMC1S19.hotmail.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751291AbbHYKSl (ORCPT ); Tue, 25 Aug 2015 06:18:41 -0400 X-TMN: [k+XNOBU9VlI6JEI0/R0pQgViaUxgX3mt] X-Originating-Email: [wanpeng.li@hotmail.com] Message-ID: Subject: Re: [PATCH] sched: fix tsk->pi_lock isn't held when do_set_cpus_allowed() To: Peter Zijlstra References: <20150825100527.GO16853@twins.programming.kicks-ass.net> CC: Ingo Molnar , linux-kernel@vger.kernel.org From: Wanpeng Li Date: Tue, 25 Aug 2015 18:18:36 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 MIME-Version: 1.0 In-Reply-To: <20150825100527.GO16853@twins.programming.kicks-ass.net> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-OriginalArrivalTime: 25 Aug 2015 10:18:40.0129 (UTC) FILETIME=[6988AF10:01D0DF1F] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1406 Lines: 43 On 8/25/15 6:05 PM, Peter Zijlstra wrote: > On Tue, Aug 25, 2015 at 03:59:54PM +0800, Wanpeng Li wrote: >> +++ b/kernel/cpuset.c >> @@ -2376,8 +2376,12 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask) >> >> void cpuset_cpus_allowed_fallback(struct task_struct *tsk) >> { >> + unsigned long flags; >> + >> rcu_read_lock(); >> + raw_spin_lock_irqsave(&tsk->pi_lock, flags); >> do_set_cpus_allowed(tsk, task_cs(tsk)->effective_cpus); >> + raw_spin_lock_irqsave(&tsk->pi_lock, flags); >> rcu_read_unlock(); > Aside from the double lock thing that was already pointed out, I think > this is wrong, because the select_task_rq() call can already have > pi_lock held. > > Taking it again would result in a deadlock. > > Consider for instance: > > try_to_wake_up() > raw_spin_lock_irqsave(->pi_lock) > select_task_rq() > select_ballback_rq() > cpuset_cpus_allowed_fallback() > raw_spin_lock_irqsave(->pi_lock) > > > The problem is with the migration path and should be fixed there. Indeed, it should be fixed in migration path. I will try to fight it out and post a patch. :) Regards, Wanpeng Li -- 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/