linux-kernel - Re: [RFC PATCH v3] Use kernfs_break_active_protection() for device online store callbacks

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Message-ID: <20140416151749.GE1257@htj.dyndns.org>
Date:	Wed, 16 Apr 2014 11:17:49 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Li Zhong <zhong@...ux.vnet.ibm.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, gregkh@...uxfoundation.org,
	rafael.j.wysocki@...el.com, toshi.kani@...com
Subject: Re: [RFC PATCH v3] Use kernfs_break_active_protection() for device
 online store callbacks

Hello,

On Wed, Apr 16, 2014 at 09:41:40AM +0800, Li Zhong wrote:
> > If so, that is
> > an actually possible deadlock, no?
> 
> Yes, but it seems to me that it is solved in commit 5e33bc41, which uses
> lock_device_hotplug_sysfs() to return a restart syscall error if not
> able to try lock the device_hotplug_lock. That also requires the device
> removing code path to take the device_hotplug_lock. 

But that patch only takes out device_hotplug_lock out of the
dependency graph and does nothing for cpu_add_remove_lock.  It seems
to be that there still is a deadlock condition involving s_active and
cpu_add_remove_lock.  Am I missing something here?

Now that kernfs has a proper mechanism to deal with it, wouldn't it
make more sense to replace 5e33bc41 with prper s_active protection
breaking?

Thanks.

-- 
tejun
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