linux-kernel - Re: drm_vm.c:drm_mmap: possible circular locking dependency detected

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Message-ID: <20100104191606.GC2597@core.coreip.homeip.net>
Date:	Mon, 4 Jan 2010 11:16:06 -0800
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Tejun Heo <tj@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Borislav Petkov <petkovbb@...glemail.com>,
	David Airlie <airlied@...ux.ie>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Greg KH <greg@...ah.com>, Al Viro <viro@...IV.linux.org.uk>
Subject: Re: drm_vm.c:drm_mmap: possible circular locking dependency detected

On Sun, Jan 03, 2010 at 03:14:18AM -0800, Eric W. Biederman wrote:
> ebiederm@...ssion.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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