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From: Tejun Heo <tj@kernel.org>
To: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>,
	LKML <linux-kernel@vger.kernel.org>,
	gregkh@linuxfoundation.org, toshi.kani@hp.com
Subject: Re: [RFC PATCH v5 2/2] Use kernfs_break_active_protection() for device online store callbacks
Date: Wed, 23 Apr 2014 12:52:44 -0400	[thread overview]
Message-ID: <20140423165244.GI4781@htj.dyndns.org> (raw)
In-Reply-To: <5357E651.2040400@intel.com>

Hello, Rafael.

On Wed, Apr 23, 2014 at 06:12:01PM +0200, Rafael J. Wysocki wrote:
> >Why add this additional global lock across multiple subsystems?
> 
> That basically is because of how eject works when it is triggered via ACPI.
> 
> It is signaled for a device at the top of a subtree.  It may be a
> container of some sort and the eject involves everything below that
> device in the ACPI namespace.  That may involve multiple subsystem
> (CPUs, memory, PCI host bridge, etc.).
> 
> We do that in two steps, offline (which can fail) and eject proper
> (which can't fail and makes all of the involved devices go away).
> All that has to be done in one go with respect to the
> sysfs-triggered offline/online and that's why the lock is there.

Ah, okay, so it's actually synchronzing across multiple subsystems.  I
think it definitely calls for more documentation.  The requirement is
pretty unusual after all.

Thanks!

-- 
tejun

  reply	other threads:[~2014-04-23 16:52 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 [this message]
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
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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