Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932479Ab2K1VdR (ORCPT ); Wed, 28 Nov 2012 16:33:17 -0500 Received: from mail-wg0-f74.google.com ([74.125.82.74]:45600 "EHLO mail-wg0-f74.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754414Ab2K1VdO (ORCPT ); Wed, 28 Nov 2012 16:33:14 -0500 From: Greg Thelen To: Tejun Heo Cc: Li Zefan , containers@lists.linux-foundation.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Aaron Durbin Subject: Re: [PATCH] cgroup: fix lockdep warning for event_control References: <1354133742-22175-1-git-send-email-gthelen@google.com> <20121128210719.GB24683@htj.dyndns.org> Date: Wed, 28 Nov 2012 13:33:11 -0800 In-Reply-To: <20121128210719.GB24683@htj.dyndns.org> (Tejun Heo's message of "Wed, 28 Nov 2012 13:07:19 -0800") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2238 Lines: 60 On Wed, Nov 28 2012, Tejun Heo wrote: > Hello, Greg. > > On Wed, Nov 28, 2012 at 12:15:42PM -0800, Greg Thelen wrote: >> @@ -4276,6 +4276,7 @@ static int cgroup_destroy_locked(struct cgroup *cgrp) >> DEFINE_WAIT(wait); >> struct cgroup_event *event, *tmp; >> struct cgroup_subsys *ss; >> + struct list_head tmp_list; > > LIST_HEAD(tmp_list); > >> >> lockdep_assert_held(&d->d_inode->i_mutex); >> lockdep_assert_held(&cgroup_mutex); >> @@ -4330,16 +4331,20 @@ static int cgroup_destroy_locked(struct cgroup *cgrp) >> /* >> * Unregister events and notify userspace. >> * Notify userspace about cgroup removing only after rmdir of cgroup >> - * directory to avoid race between userspace and kernelspace >> + * directory to avoid race between userspace and kernelspace. Use >> + * a temporary list to avoid a deadlock with cgroup_event_wake(). Since >> + * cgroup_event_wake() is called with the wait queue head locked, >> + * remove_wait_queue() cannot be called while holding event_list_lock. >> */ >> spin_lock(&cgrp->event_list_lock); >> - list_for_each_entry_safe(event, tmp, &cgrp->event_list, list) { >> + list_replace_init(&cgrp->event_list, &tmp_list); > > list_splice_init(); > > would be more conventional, I think. I used list_replace_init() because it avoided unnecessary init of tmp_list. But I have no objection to list_splice_init(). I'll repost with list_splice_init(). >> + spin_unlock(&cgrp->event_list_lock); >> + list_for_each_entry_safe(event, tmp, &tmp_list, list) { >> list_del(&event->list); > > Maybe convert this to list_del_init() while at it? I assume this isn't technically required, but defensive. Seems like we should also convert the list_del(&event->list) in cgroup_event_wake() for consistency. I'll send these in separate patch. >> remove_wait_queue(event->wqh, &event->wait); >> eventfd_signal(event->eventfd, 1); >> schedule_work(&event->remove); >> } >> - spin_unlock(&cgrp->event_list_lock); > > Thanks. -- 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/