From: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
To: Tejun Heo <tj@kernel.org>
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 00:21:33 +0200 [thread overview]
Message-ID: <5356EB6D.3010102@intel.com> (raw)
In-Reply-To: <20140422204455.GB3615@mtj.dyndns.org>
On 4/22/2014 10:44 PM, Tejun Heo wrote:
> Hello,
>
> On Tue, Apr 22, 2014 at 11:34:39AM +0800, Li Zhong wrote:
>>> Is this assumption true? If so, can we add lockdep assertions in
>>> places to verify and enforce this? If not, aren't we just feeling
>>> good when the reality is broken?
>> It seems not true ... I think there are devices that don't have the
>> online/offline concept, we just need to add it, remove it, like ethernet
>> cards.
>>
>> Maybe we could change the comments above, like:
>> /* We assume device_hotplug_lock must be acquired before
>> * removing devices, which have online/offline sysfs knob,
>> * and some locks are needed to serialize the online/offline
>> * callbacks and device removing. ...
>> ?
>>
>> And we could add lockdep assertions in cpu and memory related code? e.g.
>> remove_memory(), unregister_cpu()
>>
>> Currently, remove_memory() has comments for the function:
>>
>> * NOTE: The caller must call lock_device_hotplug() to serialize hotplug
>> * and online/offline operations before this call, as required by
>> * try_offline_node().
>> */
>>
>> maybe it could be removed with the lockdep assertion.
> I'm confused about the overall locking scheme. What's the role of
> device_hotplug_lock? Is that solely to prevent the sysfs deadlock
> issue? Or does it serve other synchronization purposes depending on
> the specific subsystem? If the former, the lock no longer needs to
> exist. The only thing necessary would be synchronization between
> device_del() deleting the sysfs file and the unbreak helper invoking
> device-specific callback. If the latter, we probably should change
> that. Sharing hotplug lock across multiple subsystems through driver
> core sounds like a pretty bad idea.
Can you please elaborate a bit?
It is there to protect hotplug operations involving multiple devices (in
different subsystems) from racing with each other. Why exactly is it bad?
Rafael
next prev parent reply other threads:[~2014-04-22 22:21 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 [this message]
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
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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