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

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Date:	Fri, 20 Apr 2012 11:31:10 +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 10:40:35AM +0100, Dave Airlie wrote:

> I've just revisited this, maybe I'm going insane but why does
> drm_global_mutex not stop this?
> 
> drm_get_pci_dev takes drm_global_mutex before calling drm_fill_in_dev
> and drm_get_minor.
> 
> Now the fops should be pointing at stub_open at this point, as we
> won't have switched to the per device fops yet,
> and one of the first things drm_stub_open does is take the
> drm_global_mutex before doing the idr lookup.
> 
> So is the problem opening some sysfs or proc file early?

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?

Anyhow, I will go back to the reporter and try and get a proper
reproduce by, there is no point in fixing something which is something
else.

-apw
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