linux-kernel - Re: [Intel-gfx] [PATCH] drm/i915: Hold struct

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Date:	Thu, 28 Jul 2011 15:50:00 -0700
From:	Keith Packard <keithp@...thp.com>
To:	Jesse Barnes <jbarnes@...tuousgeek.org>
Cc:	Daniel Vetter <daniel@...ll.ch>, Dave Airlie <airlied@...hat.com>,
	intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org
Subject: Re: [Intel-gfx] [PATCH] drm/i915: Hold struct_mutex during hotplug processing

On Wed, 27 Jul 2011 09:03:31 -0700, Jesse Barnes <jbarnes@...tuousgeek.org> wrote:
> On Wed, 27 Jul 2011 02:21:24 -0700
> Keith Packard <keithp@...thp.com> wrote:
> 
> > On Tue, 26 Jul 2011 12:12:25 -0700, Jesse Barnes <jbarnes@...tuousgeek.org> wrote:
> > 
> > > I'd like to amend my reviewed by and say the lock shouldn't be held
> > > around the call to the drm helper function.  It queues some work that
> > > also takes the mode config lock, which will break.  So you can drop it
> > > before that...  Previously I had only checked our internal driver
> > > callbacks but missed that the lock was held across the helper too.
> > 
> > So the work may get executed immediately rather than being run later at
> > some point?
> 
> It sure looks that way... but I don't remember any rule about work
> queue items having inter dependencies like this.

Sounds fine; I've stuck a fixup that moves the mutex_unlock:

 		if (encoder->hot_plug)
 			encoder->hot_plug(encoder);
 
+	mutex_unlock(&mode_config->mutex);
+
 	/* Just fire off a uevent and let userspace tell us what to do */
 	drm_helper_hpd_irq_event(dev);
-
-	mutex_unlock(&mode_config->mutex);
 }

-- 
keith.packard@...el.com

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