linux-kernel - Re: [Bug #12574] possible circular locking dependency detected

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Date:	Tue, 10 Feb 2009 14:41:56 -0800
From:	Eric Anholt <eric@...olt.net>
To:	"Michael S. Tsirkin" <m.s.tsirkin@...il.com>
Cc:	Dave Airlie <airlied@...ux.ie>, dri-devel@...ts.sourceforge.net,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: [Bug #12574] possible circular locking dependency detected

On Wed, 2009-02-11 at 00:37 +0200, Michael S. Tsirkin wrote:
> Dave, dri guys,
> Could you take a look at this circular dependency please (below)?  I
> observe it when suspending laptop with radeon drm loaded and with
> lockdep enabled. It seems that the root of the problem is that
> various vm ops such as drm_vm_open, drm_mmap) are called with mm
> semaphore taken, and take dev->struct_mutex. On the other hand,
> drm_rmmap_locked is called with dev->struct_mutex, and calls mtrr_del
> which depends on mm semaphore indirectly.
> 
> What do you think?

Yes, there are real lock inversions now due to the GTT mmap code.  It's
going to be a pain to fix (I tried getting the mmap_sem -> struct_mutex
path to go away, but the fact that mmap_sem is held over the fault
handler pretty much kills that).  It's high on the list, though.

-- 
Eric Anholt
eric@...olt.net                         eric.anholt@...el.com



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