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Date: Mon, 4 Jan 2010 11:16:06 -0800
From: Dmitry Torokhov <dmitry.torokhov@gmail.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Tejun Heo <tj@kernel.org>, Linus Torvalds <torvalds@linux-foundation.org>,
       KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
       Borislav Petkov <petkovbb@googlemail.com>,
       David Airlie <airlied@linux.ie>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Greg KH <greg@kroah.com>, Al Viro <viro@ZenIV.linux.org.uk>
Subject: Re: drm_vm.c:drm_mmap: possible circular locking dependency detected
Message-ID: <20100104191606.GC2597@core.coreip.homeip.net>
References: <alpine.LFD.2.00.0912301348320.11961@localhost.localdomain>
 <m1fx6rtu31.fsf@fess.ebiederm.org>
 <alpine.LFD.2.00.0912311043330.11961@localhost.localdomain>
 <m11vi9c0td.fsf@fess.ebiederm.org>
 <4B3EB687.7000005@kernel.org>
 <m17hs0xjmn.fsf@fess.ebiederm.org>
 <4B3FE586.7020109@kernel.org>
 <20100103074745.GA2314@core.coreip.homeip.net>
 <m1tyv3sbg4.fsf@fess.ebiederm.org>
 <m1d41rsanp.fsf@fess.ebiederm.org>
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On Sun, Jan 03, 2010 at 03:14:18AM -0800, Eric W. Biederman wrote:
> ebiederm@xmission.com (Eric W. Biederman) writes:
> 
> > What to do about it is another question.   It has just recently come to my
> > attention that we have more events like this
> 
> In the specific case of serio what gets us in trouble is
> the call to sysfs_remove_group.
> 
> If instead of independent calls to sysfs_create_group/sysfs_remove_group,
> you could move the groups into a list on dev->groups than we could solve
> two problems.
> 
> - Userspace would see all of the attributes when the hotplug event is
>   fired remove races.
> 
> - We would not hold serio->drv_mutex over sysfs_remove_group so there
>   would not be a possible deadlock on device removal.
> 
> Does that change sound possible?

No, because attributes in question belong to driver+device combo. The
device will not go away when driver is unbound but we do want to remove
attributes.

-- 
Dmitry
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