Re: [PATCH] drm/i915: Preallocate request before access of the ring

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, Apr 30, 2015 at 01:54:41PM +0100, Dave Gordon wrote:
> On 29/04/15 17:10, yu.dai@intel.com wrote:
> > From: Alex Dai <yu.dai@intel.com>
> > 
> > This is to avoid bad IO access caused by writing NOOP to wrap the
> > ring buffer whilst ring is unpinned.
> > 
> > Signed-off-by: Alex Dai <yu.dai@intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_lrc.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> > index 732fd63..3e8fcfd 100644
> > --- a/drivers/gpu/drm/i915/intel_lrc.c
> > +++ b/drivers/gpu/drm/i915/intel_lrc.c
> > @@ -803,12 +803,12 @@ static int intel_logical_ring_begin(struct intel_ringbuffer *ringbuf,
> >  	if (ret)
> >  		return ret;
> >  
> > -	ret = logical_ring_prepare(ringbuf, ctx, num_dwords * sizeof(uint32_t));
> > +	/* Preallocate the olr before touching the ring */
> > +	ret = i915_gem_request_alloc(ring, ctx);
> >  	if (ret)
> >  		return ret;
> >  
> > -	/* Preallocate the olr before touching the ring */
> > -	ret = i915_gem_request_alloc(ring, ctx);
> > +	ret = logical_ring_prepare(ringbuf, ctx, num_dwords * sizeof(uint32_t));
> >  	if (ret)
> >  		return ret;
> 
> Reviewed-by: Dave Gordon <david.s.gordon@intel.com>
> 
> with input also from John Harrison <john.c.harrison@intel.com>, who
> would like to point out that this will be superceded by the Anti-OLR
> patches already posted. (In that model, the request will be allocated
> much earlier, and passed around explicitly rather than dangling from the
> context).

Do we need this for execlist in general, i.e. cc: stable? Where's the bug
report/igt testcase?

For serious-looking bugs please add more details like that to the commit
message, otherwise maintainers have no idea where to apply a patch.

Thanks, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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