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From: Tejun Heo <tj@kernel.org>
To: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
	gregkh@linuxfoundation.org, rafael.j.wysocki@intel.com,
	toshi.kani@hp.com
Subject: Re: [RFC PATCH v5 1/2] Use lock_device_hotplug() in cpu_probe_store() and cpu_release_store()
Date: Thu, 24 Apr 2014 10:32:08 -0400	[thread overview]
Message-ID: <20140424143208.GB14460@htj.dyndns.org> (raw)
In-Reply-To: <1398328643.2805.102.camel@ThinkPad-T5421.cn.ibm.com>

Hello,

On Thu, Apr 24, 2014 at 04:37:23PM +0800, Li Zhong wrote:
> On Wed, 2014-04-23 at 10:39 -0400, Tejun Heo wrote:
> After thinking it harder, I still couldn't see ABBA here ... 
> 
> the active protection taken here is for "probe/release" which will not
> be waited for removing something like "online" under cpu#? Or my
> assumption that s_active for different files are different locks are
> completely wrong? Or I missed something else? 

I'm probably confused about the locking.  I was thinking a scenario
like the following.

A. CPU on/offline

   grabs s_active protection of online node
   grabs cpu subsys mutex
   perform on/offline
   releases cpu subsys mutex
   releases s_active protection of online node

B. CPU release

   grabs s_active protection of release node
   grabs cpu subsys mutex
   performs removal of the CPU
   removes the online node
   releases cpu subsys mutex
   releases s_active protection of release node

A nests cpu subsys mutex under s_active of the online node.  B nests
s_active of the online node under the cpu subsys mutex.  What am I
missing?

Thanks.

-- 
tejun

  reply	other threads:[~2014-04-24 14:32 UTC|newest]

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-04-10  9:18 [RFC PATCH] Suppress a device hot remove related lockdep warning Li Zhong
2014-04-10 13:31 ` Tejun Heo
2014-04-11  4:10   ` [RFC PATCH v2] Use kernfs_break_active_protection() for device online store callbacks Li Zhong
2014-04-11 10:26     ` Tejun Heo
2014-04-14  7:47       ` [RFC PATCH v3] " Li Zhong
2014-04-14 20:13         ` Tejun Heo
2014-04-15  2:44           ` Li Zhong
2014-04-15 14:50             ` Tejun Heo
2014-04-16  1:41               ` Li Zhong
2014-04-16 15:17                 ` Tejun Heo
2014-04-17  3:05                   ` Li Zhong
2014-04-17 15:06                     ` Tejun Heo
2014-04-17  6:50                   ` [RFC PATCH v4] " Li Zhong
2014-04-17 15:17                     ` Tejun Heo
2014-04-18  8:33                       ` Li Zhong
2014-04-21  9:20                       ` [RFC PATCH v5 1/2] Use lock_device_hotplug() in cpu_probe_store() and cpu_release_store() Li Zhong
2014-04-21  9:23                         ` [RFC PATCH v5 2/2] Use kernfs_break_active_protection() for device online store callbacks Li Zhong
2014-04-21 22:46                           ` Tejun Heo
2014-04-22  3:34                             ` Li Zhong
2014-04-22 10:11                               ` Rafael J. Wysocki
2014-04-23  1:50                                 ` Li Zhong
2014-04-23 10:54                                   ` Rafael J. Wysocki
2014-04-24  1:13                                     ` Li Zhong
2014-04-22 20:44                               ` Tejun Heo
2014-04-22 22:21                                 ` Rafael J. Wysocki
2014-04-23 14:23                                   ` Tejun Heo
2014-04-23 16:12                                     ` Rafael J. Wysocki
2014-04-23 16:52                                       ` Tejun Heo
2014-04-24  8:59                                       ` Li Zhong
2014-04-24 10:02                                         ` Rafael J. Wysocki
2014-04-25  1:46                                           ` Li Zhong
2014-04-25 12:47                                             ` Rafael J. Wysocki
2014-04-28  1:49                                               ` Li Zhong
2014-04-23  5:03                                 ` Li Zhong
2014-04-23 10:58                                   ` Rafael J. Wysocki
2014-04-24  1:33                                     ` Li Zhong
2014-05-09  8:35                               ` Li Zhong
2014-05-09  8:40                                 ` [RFC PATCH v6 1/2 ] Use lock_device_hotplug() in cpu_probe_store() and cpu_release_store() Li Zhong
2014-05-09  8:40                                   ` [RFC PATCH v6 2/2] Implement lock_device_hotplug_sysfs() by breaking active protection Li Zhong
2014-04-21 22:38                         ` [RFC PATCH v5 1/2] Use lock_device_hotplug() in cpu_probe_store() and cpu_release_store() Tejun Heo
2014-04-22  2:29                           ` Li Zhong
2014-04-22 20:40                             ` Tejun Heo
2014-04-23  2:00                               ` Li Zhong
2014-04-23 14:39                                 ` Tejun Heo
2014-04-24  8:37                                   ` Li Zhong
2014-04-24 14:32                                     ` Tejun Heo [this message]
2014-04-25  1:56                                       ` Li Zhong
2014-04-25 12:28                                         ` Tejun Heo
2014-04-28  0:51                                           ` Li Zhong

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