linux-kernel - Re: [PATCH 0/1] [RFC] DRM locking issues during early open

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Date:	Fri, 20 Apr 2012 18:25:40 +0100
From:	Andy Whitcroft <apw@...onical.com>
To:	Dave Airlie <airlied@...il.com>
Cc:	David Airlie <airlied@...ux.ie>, dri-devel@...ts.freedesktop.org,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Bryce Harrington <bryce@...onical.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/1] [RFC] DRM locking issues during early open

On Fri, Apr 20, 2012 at 11:34:43AM +0100, Dave Airlie wrote:
> >
> > I may be reading things wrong but the initialisation does indeed hold
> > drm_global_mutex, but and back when this first occured we would have
> > been using kernel_lock() which was at least partially reentrant right?
> 
> Yup if we slept with the BKL held we'd have allowed others to get past it,
> but also I introduced the global mutex in pci a while back

Yeah I have managed to get access to more details on the bug, and
actually we are opening the drm device successfully, we then attempt a
DRM_SETVERSION ioctl on it and it is that that appears to fail both for
1.4 and 1.1.

It is somewhat perplexing to understand how that is possible, though I
will note that the stub f_ops do not contain an ioctl op but I cannot
see any mechanism by which we might return a validly open file without
putting the driver specific ops in it.

-apw
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