linux-kernel - Re: [PATCH] cgroup: fix lockdep warning for event

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20121128210719.GB24683@htj.dyndns.org>
Date:	Wed, 28 Nov 2012 13:07:19 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Greg Thelen <gthelen@...gle.com>
Cc:	Li Zefan <lizefan@...wei.com>,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org, Aaron Durbin <adurbin@...gle.com>
Subject: Re: [PATCH] cgroup: fix lockdep warning for event_control

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.

> +	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?

>  		remove_wait_queue(event->wqh, &event->wait);
>  		eventfd_signal(event->eventfd, 1);
>  		schedule_work(&event->remove);
>  	}
> -	spin_unlock(&cgrp->event_list_lock);

Thanks.

-- 
tejun
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/