From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754001Ab3CFHBk (ORCPT ); Wed, 6 Mar 2013 02:01:40 -0500 Received: from szxga02-in.huawei.com ([119.145.14.65]:63939 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752575Ab3CFHBf (ORCPT ); Wed, 6 Mar 2013 02:01:35 -0500 Message-ID: <5136E9A4.7000201@huawei.com> Date: Wed, 6 Mar 2013 15:00:52 +0800 From: Li Zefan User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:17.0) Gecko/20130215 Thunderbird/17.0.3 MIME-Version: 1.0 To: Tejun Heo CC: "Kirill A. Shutemov" , LKML , Cgroups Subject: Re: [PATCH] cgroup: make cgrp->event_list_lock irqsafe References: <5136B7C1.6030403@huawei.com> <20130306062224.GJ1227@htj.dyndns.org> In-Reply-To: <20130306062224.GJ1227@htj.dyndns.org> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.135.68.215] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2013/3/6 14:22, Tejun Heo wrote: > Hello, Li. > > On Wed, Mar 06, 2013 at 11:28:01AM +0800, Li Zefan wrote: >> cgroup_event_wake() is called with hardirq-safe wqh->lock held, so >> the nested cgrp->event_list_lock should also be hardirq-safe. >> >> Fortunately I don't think the deadlock can happen in real life. >> >> Lockdep never complained, maybe because it never found wqh->lock was >> held in irq context? > > Why should wqh->lock be hard-irq-safe? Is it actually grabbed from > irq context? becase cgroup_event_wake() is a callback to a wait queue, and it's wake_up() that acquires wqh->lock with irq disabled. > Locks which are grabbed with irq disabled aren't > necessarily irq context locks as that doesn't lead to deadlocks. They > need to be actually grabbed from irq context. > > Thanks. >