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From: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
To: Neil Horman <nhorman-2XuSBdqkA4R54TAoqtyWWQ@public.gmane.org>
Cc: Daniel Wagner <wagi-kQCPcA+X3s7YtjvyW6yDsg@public.gmane.org>,
	netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	Daniel Wagner
	<daniel.wagner-98C5kh4wR6ohFhg+JK9F0w@public.gmane.org>,
	"David S. Miller" <davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org>,
	Gao feng <gaofeng-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>,
	Jamal Hadi Salim <jhs-jkUAjuhPggJWk0Htik3J/w@public.gmane.org>,
	John Fastabend
	<john.r.fastabend-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>,
	Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>,
	Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Subject: Re: [PATCH v1 3/5] cgroup: Protect access to task_cls_classid() when built as module
Date: Tue, 21 Aug 2012 13:12:33 +0400	[thread overview]
Message-ID: <50335101.5030109@parallels.com> (raw)
In-Reply-To: <20120820170342.GC1734-B26myB8xz7F8NnZeBjwnZQMhkBWG/bsMQH7oEaQurus@public.gmane.org>

On 08/20/2012 09:03 PM, Neil Horman wrote:
>>> 2) Keep a separate internal counter to track the number of cgroup instances
>>> > > so that you only inc the static key on the first create and dec it on the last
>>> > > delete.
>> > 
>> > If I got you right, than this would not be different then direclty using
>> > static_key_slow_[inc|dec].
>> > 
> As long as a cgroup subsystems ->destroy method is only called when the
> subsystem is being removed, then I think thats correct.  I'm not 100% sure thats
> the case though.
> 
THAT is correct, but not the call itself. ->destroy() is called with the
cgroup_lock held, and there is a lockdep dependency created by cpuset
that prevents the cpu_hotplug lock, taken by static branch updates, to
be taken inside cgroup_lock.

So unless cpuset is fixed - which is a major work, we can't do
static_branch updates while holding the cgroup_lock.


WARNING: multiple messages have this Message-ID (diff)
From: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
To: Neil Horman <nhorman-2XuSBdqkA4R54TAoqtyWWQ@public.gmane.org>
Cc: Daniel Wagner <wagi-kQCPcA+X3s7YtjvyW6yDsg@public.gmane.org>,
	<netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	<cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	Daniel Wagner
	<daniel.wagner-98C5kh4wR6ohFhg+JK9F0w@public.gmane.org>,
	"David S. Miller" <davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org>,
	Gao feng <gaofeng-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>,
	Jamal Hadi Salim <jhs-jkUAjuhPggJWk0Htik3J/w@public.gmane.org>,
	John Fastabend
	<john.r.fastabend-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>,
	Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>,
	Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Subject: Re: [PATCH v1 3/5] cgroup: Protect access to task_cls_classid() when built as module
Date: Tue, 21 Aug 2012 13:12:33 +0400	[thread overview]
Message-ID: <50335101.5030109@parallels.com> (raw)
In-Reply-To: <20120820170342.GC1734-B26myB8xz7F8NnZeBjwnZQMhkBWG/bsMQH7oEaQurus@public.gmane.org>

On 08/20/2012 09:03 PM, Neil Horman wrote:
>>> 2) Keep a separate internal counter to track the number of cgroup instances
>>> > > so that you only inc the static key on the first create and dec it on the last
>>> > > delete.
>> > 
>> > If I got you right, than this would not be different then direclty using
>> > static_key_slow_[inc|dec].
>> > 
> As long as a cgroup subsystems ->destroy method is only called when the
> subsystem is being removed, then I think thats correct.  I'm not 100% sure thats
> the case though.
> 
THAT is correct, but not the call itself. ->destroy() is called with the
cgroup_lock held, and there is a lockdep dependency created by cpuset
that prevents the cpu_hotplug lock, taken by static branch updates, to
be taken inside cgroup_lock.

So unless cpuset is fixed - which is a major work, we can't do
static_branch updates while holding the cgroup_lock.

  parent reply	other threads:[~2012-08-21  9:12 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-08-17 14:58 [PATCH v1 0/5] cgroup: Assign subsystem IDs during compile time Daniel Wagner
     [not found] ` <1345215494-9181-1-git-send-email-wagi-kQCPcA+X3s7YtjvyW6yDsg@public.gmane.org>
2012-08-17 14:58   ` [PATCH v1 1/5] cgroup: Use empty task_cls_classid() when !CONFIG_NET_CLS(_MODULE) Daniel Wagner
2012-08-17 14:58   ` [PATCH v1 2/5] cgroup: Move sock_update_classid() decleration to cls_cgroup.h Daniel Wagner
2012-08-17 14:58   ` [PATCH v1 3/5] cgroup: Protect access to task_cls_classid() when built as module Daniel Wagner
     [not found]     ` <1345215494-9181-4-git-send-email-wagi-kQCPcA+X3s7YtjvyW6yDsg@public.gmane.org>
2012-08-17 18:28       ` Neil Horman
2012-08-20  0:59         ` Li Zefan
2012-08-20  0:59           ` Li Zefan
     [not found]           ` <50318BF9.2080803-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
2012-08-20 11:08             ` Neil Horman
     [not found]         ` <20120817182855.GA11607-B26myB8xz7F8NnZeBjwnZQMhkBWG/bsMQH7oEaQurus@public.gmane.org>
2012-08-20 11:29           ` Daniel Wagner
     [not found]             ` <20120820112938.GA22415-rjQKm2AMs/APuY3F5OKgMy7zKzJi9e1+kcYEyfhdaNw@public.gmane.org>
2012-08-20 11:33               ` Glauber Costa
2012-08-20 11:33                 ` Glauber Costa
2012-08-20 17:03               ` Neil Horman
     [not found]                 ` <20120820170342.GC1734-B26myB8xz7F8NnZeBjwnZQMhkBWG/bsMQH7oEaQurus@public.gmane.org>
2012-08-21  9:12                   ` Glauber Costa [this message]
2012-08-21  9:12                     ` Glauber Costa
     [not found]                     ` <50335101.5030109-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
2012-08-23  9:12                       ` Daniel Wagner
     [not found]                         ` <5035F3FC.202-kQCPcA+X3s7YtjvyW6yDsg@public.gmane.org>
2012-08-23  9:12                           ` Glauber Costa
2012-08-23  9:12                             ` Glauber Costa
2012-08-17 14:58   ` [PATCH v1 4/5] cgroup: Protect access to task_netprioidx() " Daniel Wagner
2012-08-17 14:58   ` [PATCH v1 5/5] cgroup: Assign subsystem IDs during compile time Daniel Wagner

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