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

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Message-ID: <m1ljgfvjcy.fsf@fess.ebiederm.org>
Date:	Sat, 02 Jan 2010 21:38:05 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Tejun Heo <tj@...nel.org>
Cc:	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>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>
Subject: Re: drm_vm.c:drm_mmap: possible circular locking dependency detected

Tejun Heo <tj@...nel.org> writes:

> It's interesting that the above cases arn't common drivers.  AFAICS,
> the problem cases would usually be cases like above where the user is
> a rather complex software entity or drivers which implement some form
> of self detaching via sysfs.  For the former group, I agree that
> splitting deleting and draining (or simply skipping the draining part
> or active reference counting both of which basically achieve the same
> thing) would be an easy way out as it would be generally easy to leave
> the data structures dangling till the references go away.
>
> How about simply introducing an interface to mark sysfs nodes which
> don't require active reference counting and using them on those nodes?

That might work.  However it does not seem to address the case of
bond_sysfs, especially with someone doing rmmod bonding.

I think the brainstorm is on the right track.  I think we just need to look
at a few more cases in depth so that we can see a pattern and generalize
what can be done.

Eric
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