Re: [PATCH 06/16] drm: Protect the master management with a drm_device::master_mutex

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Mar 26, 2014 at 09:40:18PM +0100, Thomas Hellstrom wrote:
> On 03/26/2014 08:08 PM, David Herrmann wrote:
> > "struct_mutex" is used to serialize all entry-points into
> > the drm-device (and thus the driver) and also, often implicitly, as
> > spin-lock for "struct drm_device" data protection.
> 
> No. DRM locking was added as an after-though, and is a horrendous mess.
> Nobody really knows what's protecting what, and that has caused a lot of
> grief in the past. Probably most so for the Intel driver that relied
> (relies?) on the struct_mutex to protect everything. The
> drm_global_mutex is used to serialize the non-lock-audited entry points
> into the drm device. The struct_mutex is used for data protection of
> most core drm structures and serializing here and there. Modern drivers
> have no locks held when entering their ioctls. Also we should not
> confuse mutexes and spinlocks in this context, as they have very
> different semantics.

As the guy who gets to live the locking mess called dev->struct_mutex I
holeheartedly welcome any efforts to split out clear subparts away from
it. I actually had this very idea of adding a master-data related mutex on
my todo. I'll try to review this later if I get around, but definitely
Acked!
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch