Re: [PATCH] cgroup: make cgrp->event_list_lock irqsafe

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From: Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
To: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Cc: "Kirill A. Shutemov"
	<kirill-oKw7cIdHH8eLwutG50LtGA@public.gmane.org>,
	LKML <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	Cgroups <cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
Subject: Re: [PATCH] cgroup: make cgrp->event_list_lock irqsafe
Date: Wed, 6 Mar 2013 15:00:52 +0800	[thread overview]
Message-ID: <5136E9A4.7000201@huawei.com> (raw)
In-Reply-To: <20130306062224.GJ1227-Gd/HAXX7CRxy/B6EtB590w@public.gmane.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.
>

WARNING: multiple messages have this Message-ID (diff)

From: Li Zefan <lizefan@huawei.com>
To: Tejun Heo <tj@kernel.org>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>,
	LKML <linux-kernel@vger.kernel.org>,
	Cgroups <cgroups@vger.kernel.org>
Subject: Re: [PATCH] cgroup: make cgrp->event_list_lock irqsafe
Date: Wed, 6 Mar 2013 15:00:52 +0800	[thread overview]
Message-ID: <5136E9A4.7000201@huawei.com> (raw)
In-Reply-To: <20130306062224.GJ1227@htj.dyndns.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.
>

next prev parent reply	other threads:[~2013-03-06  7:00 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-03-06  3:28 [PATCH] cgroup: make cgrp->event_list_lock irqsafe Li Zefan
2013-03-06  6:22 ` Tejun Heo
     [not found]   ` <20130306062224.GJ1227-Gd/HAXX7CRxy/B6EtB590w@public.gmane.org>
2013-03-06  7:00     ` Li Zefan [this message]
2013-03-06  7:00       ` Li Zefan
     [not found]       ` <5136E9A4.7000201-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
2013-03-06  7:02         ` Tejun Heo
2013-03-06  7:02           ` Tejun Heo
     [not found]           ` <CAOS58YN9K9OrvvdZjUV9dFOP=SpJYgeyPp0Y5yipNE47osqXpQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2013-03-06  7:15             ` Li Zefan
2013-03-06  7:15               ` Li Zefan
     [not found]               ` <5136ED2F.8080400-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
2013-03-06  7:21                 ` Tejun Heo
2013-03-06  7:21                   ` Tejun Heo
     [not found]                   ` <CAOS58YNJd557hGDMGqavp8eq+B9x5WExCcpW+CwZ8dUainjUUw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2013-03-06  7:23                     ` Tejun Heo
2013-03-06  7:23                       ` Tejun Heo

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