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From: Tejun Heo <tj@kernel.org>
To: Waiman Long <longman@redhat.com>
Cc: Zefan Li <lizefan.x@bytedance.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	cgroups@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] cgroup: Fix incorrect warning from cgroup_apply_control_disable()
Date: Mon, 13 Sep 2021 08:05:55 -1000	[thread overview]
Message-ID: <YT+TA6ItnF9xM3cR@slm.duckdns.org> (raw)
In-Reply-To: <20210910024256.7615-1-longman@redhat.com>

Hello,

On Thu, Sep 09, 2021 at 10:42:55PM -0400, Waiman Long wrote:
> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
> index 881ce1470beb..e31bca9fcd46 100644
> --- a/kernel/cgroup/cgroup.c
> +++ b/kernel/cgroup/cgroup.c
> @@ -3140,7 +3140,16 @@ static void cgroup_apply_control_disable(struct cgroup *cgrp)
>  			if (!css)
>  				continue;
>  
> -			WARN_ON_ONCE(percpu_ref_is_dying(&css->refcnt));
> +			/*
> +			 * A kill_css() might have been called previously, but
> +			 * the css may still linger for a while before being
> +			 * removed. Skip it in this case.
> +			 */
> +			if (percpu_ref_is_dying(&css->refcnt)) {
> +				WARN_ON_ONCE(css->parent &&
> +					cgroup_ss_mask(dsct) & (1 << ss->id));
> +				continue;
> +			}

This warning did help me catch some gnarly bugs. Any chance we can keep it
for normal cases and elide it just for remounting?

Thanks.

-- 
tejun

WARNING: multiple messages have this Message-ID (diff)
From: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
To: Waiman Long <longman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Cc: Zefan Li <lizefan.x-EC8Uxl6Npydl57MIdRCFDg@public.gmane.org>,
	Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>,
	Juri Lelli <juri.lelli-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH 1/2] cgroup: Fix incorrect warning from cgroup_apply_control_disable()
Date: Mon, 13 Sep 2021 08:05:55 -1000	[thread overview]
Message-ID: <YT+TA6ItnF9xM3cR@slm.duckdns.org> (raw)
In-Reply-To: <20210910024256.7615-1-longman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>

Hello,

On Thu, Sep 09, 2021 at 10:42:55PM -0400, Waiman Long wrote:
> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
> index 881ce1470beb..e31bca9fcd46 100644
> --- a/kernel/cgroup/cgroup.c
> +++ b/kernel/cgroup/cgroup.c
> @@ -3140,7 +3140,16 @@ static void cgroup_apply_control_disable(struct cgroup *cgrp)
>  			if (!css)
>  				continue;
>  
> -			WARN_ON_ONCE(percpu_ref_is_dying(&css->refcnt));
> +			/*
> +			 * A kill_css() might have been called previously, but
> +			 * the css may still linger for a while before being
> +			 * removed. Skip it in this case.
> +			 */
> +			if (percpu_ref_is_dying(&css->refcnt)) {
> +				WARN_ON_ONCE(css->parent &&
> +					cgroup_ss_mask(dsct) & (1 << ss->id));
> +				continue;
> +			}

This warning did help me catch some gnarly bugs. Any chance we can keep it
for normal cases and elide it just for remounting?

Thanks.

-- 
tejun

  parent reply	other threads:[~2021-09-13 18:06 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-10  2:42 [PATCH 1/2] cgroup: Fix incorrect warning from cgroup_apply_control_disable() Waiman Long
2021-09-10  2:42 ` Waiman Long
2021-09-10  2:42 ` [PATCH 2/2] cgroup/cpuset: Change references of cpuset_mutex to cpuset_rwsem Waiman Long
2021-09-10  2:42   ` Waiman Long
2021-09-13 18:06   ` Tejun Heo
2021-09-13 18:05 ` Tejun Heo [this message]
2021-09-13 18:05   ` [PATCH 1/2] cgroup: Fix incorrect warning from cgroup_apply_control_disable() Tejun Heo
2021-09-13 18:35   ` Waiman Long
2021-09-13 18:35     ` Waiman Long
2021-09-13 18:40     ` Tejun Heo
2021-09-13 18:40       ` Tejun Heo
2021-09-13 18:43     ` Waiman Long
2021-09-13 18:43       ` Waiman Long
2021-09-13 18:45       ` Tejun Heo
2021-09-13 18:45         ` Tejun Heo
2021-09-13 18:46         ` Waiman Long
2021-09-13 18:46           ` Waiman Long

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