From: Li Zhong <zhong@linux.vnet.ibm.com>
To: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Tejun Heo <tj@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
gregkh@linuxfoundation.org, rafael.j.wysocki@intel.com,
toshi.kani@hp.com
Subject: Re: [RFC PATCH v5 2/2] Use kernfs_break_active_protection() for device online store callbacks
Date: Thu, 24 Apr 2014 09:33:14 +0800 [thread overview]
Message-ID: <1398303194.2805.64.camel@ThinkPad-T5421.cn.ibm.com> (raw)
In-Reply-To: <10378860.X4mJXjBVbJ@vostro.rjw.lan>
On Wed, 2014-04-23 at 12:58 +0200, Rafael J. Wysocki wrote:
> On Wednesday, April 23, 2014 01:03:42 PM Li Zhong wrote:
> > On Tue, 2014-04-22 at 16:44 -0400, 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.
> >
> > I think it's the latter.
>
> Actually, no, this is not the case if I understand you correctly.
Oh, Sorry, I didn't read carefully. Yes, it's not specific subsystem.
After seeing your reply, I understand it is for protecting device hot
remove involving multiple subsystems.
>
> > I think device_{on|off}line is better to be
> > done in some sort of lock which prevents the device from being removed,
> > including some preparation work that needs be done before device_del().
>
> Quite frankly, you should be confident that you understand the code you're
> trying to modify or please don't touch it.
>
> I'll have a deeper look at this issue later today or tomorrow and will get
> back to you then.
Ok, thank you,
Zhong
>
> Thanks!
>
next prev parent reply other threads:[~2014-04-24 1:33 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 [this message]
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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