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

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Date:	Sun, 03 Jan 2010 03:14:18 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Dmitry Torokhov <dmitry.torokhov@...il.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

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?

Eric


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