[Intel-gfx] [PATCH v2] drm/i915: Snapshot seqno of most recently submitted request.

[Daniel Vetter]

On Thu, Jul 09, 2015 at 04:07:05PM +0100, Chris Wilson wrote:
> On Thu, Jul 09, 2015 at 03:30:57PM +0100, Tomas Elf wrote:
> > The hang checker needs to inspect whether or not the ring request list is empty
> > as well as if the given engine has reached or passed the most recently
> > submitted request. The problem with this is that the hang checker cannot grab
> > the struct_mutex, which is required in order to safely inspect requests since
> > requests might be deallocated during inspection. In the past we've had kernel
> > panics due to this very unsynchronized access in the hang checker.
> > 
> > One solution to this problem is to not inspect the requests directly since
> > we're only interested in the seqno of the most recently submitted request - not
> > the request itself. Instead the seqno of the most recently submitted request is
> > stored separately, which the hang checker then inspects, circumventing the
> > issue of synchronization from the hang checker entirely.
> > 
> > v2 (Chris Wilson):
> > - Pass current engine seqno to ring_idle() from i915_hangcheck_elapsed() rather
> > than compute it over again.
> > - Remove extra whitespace.
> > 
> > Issue: VIZ-5998
> > Signed-off-by: Tomas Elf <tomas.elf at intel.com>
> 
> Yup, that is a nice simple fix by partially reverting the
> s/seqno/requests/ change (and improving upon it in the process).
> 
> We should mention
> 
> Fixes commit 44cdd6d219bc64f6810b8ed0023a4d4db9e0fe68
> Author: John Harrison <John.C.Harrison at Intel.com>
> Date:   Mon Nov 24 18:49:40 2014 +0000
> 
>     drm/i915: Convert 'ring_idle()' to use requests not seqnos
> 
> and
> Cc: stable at vger.kernel.org
> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>

Added and applied to -fixes, thanks.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch