[PATCH] drm/i915: Use DRIVER_NAME for tracing unattached requests

[Daniel Vetter]

On Thu, May 20, 2021 at 08:35:14AM +0100, Matthew Auld wrote:
> From: Chris Wilson <chris at chris-wilson.co.uk>
> 
> The first tracepoint for a request is trace_dma_fence_init called before
> we have associated the request with a device. The tracepoint uses
> fence->ops->get_driver_name() as a pretty name, and as we try to report
> the device name this oopses as it is then NULL. Support the early
> tracepoint by reporting the DRIVER_NAME instead of the actual device
> name.
> 
> Note that rq->engine remains during the course of request recycling
> (SLAB_TYPESAFE_BY_RCU). For the physical engines, the pointer remains
> valid, however a virtual engine may be destroyed after the request is
> retired. If we process a preempt-to-busy completed request along the
> virtual engine, we should make sure we mark the request as no longer
> belonging to the virtual engine to remove the dangling pointers from the
> tracepoint.

Why can't we assign the request beforehand? The idea behind these
tracepoints is that they actually match up, if trace_dma_fence_init is
different, then we're breaking that.
-Daniel

> 
> Fixes: 855e39e65cfc ("drm/i915: Initialise basic fence before acquiring seqno")
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
> Cc: Chintan M Patel <chintan.m.patel at intel.com>
> Cc: Andi Shyti <andi.shyti at intel.com>
> Cc: <stable at vger.kernel.org> # v5.7+
> Signed-off-by: Matthew Auld <matthew.auld at intel.com>
> ---
>  .../drm/i915/gt/intel_execlists_submission.c  | 20 ++++++++++++++-----
>  drivers/gpu/drm/i915/i915_request.c           |  7 ++++++-
>  2 files changed, 21 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
> index de124870af44..75604e927d34 100644
> --- a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
> +++ b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
> @@ -3249,6 +3249,18 @@ static struct list_head *virtual_queue(struct virtual_engine *ve)
>  	return &ve->base.execlists.default_priolist.requests;
>  }
>  
> +static void
> +virtual_submit_completed(struct virtual_engine *ve, struct i915_request *rq)
> +{
> +	GEM_BUG_ON(!__i915_request_is_complete(rq));
> +	GEM_BUG_ON(rq->engine != &ve->base);
> +
> +	__i915_request_submit(rq);
> +
> +	/* Remove the dangling pointer to the stale virtual engine */
> +	WRITE_ONCE(rq->engine, ve->siblings[0]);
> +}
> +
>  static void rcu_virtual_context_destroy(struct work_struct *wrk)
>  {
>  	struct virtual_engine *ve =
> @@ -3265,8 +3277,7 @@ static void rcu_virtual_context_destroy(struct work_struct *wrk)
>  
>  		old = fetch_and_zero(&ve->request);
>  		if (old) {
> -			GEM_BUG_ON(!__i915_request_is_complete(old));
> -			__i915_request_submit(old);
> +			virtual_submit_completed(ve, old);
>  			i915_request_put(old);
>  		}
>  
> @@ -3538,13 +3549,12 @@ static void virtual_submit_request(struct i915_request *rq)
>  
>  	/* By the time we resubmit a request, it may be completed */
>  	if (__i915_request_is_complete(rq)) {
> -		__i915_request_submit(rq);
> +		virtual_submit_completed(ve, rq);
>  		goto unlock;
>  	}
>  
>  	if (ve->request) { /* background completion from preempt-to-busy */
> -		GEM_BUG_ON(!__i915_request_is_complete(ve->request));
> -		__i915_request_submit(ve->request);
> +		virtual_submit_completed(ve, ve->request);
>  		i915_request_put(ve->request);
>  	}
>  
> diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
> index 970d8f4986bb..aa124adb1051 100644
> --- a/drivers/gpu/drm/i915/i915_request.c
> +++ b/drivers/gpu/drm/i915/i915_request.c
> @@ -61,7 +61,12 @@ static struct i915_global_request {
>  
>  static const char *i915_fence_get_driver_name(struct dma_fence *fence)
>  {
> -	return dev_name(to_request(fence)->engine->i915->drm.dev);
> +	struct i915_request *rq = to_request(fence);
> +
> +	if (unlikely(!rq->engine)) /* not yet attached to any device */
> +		return DRIVER_NAME;
> +
> +	return dev_name(rq->engine->i915->drm.dev);
>  }
>  
>  static const char *i915_fence_get_timeline_name(struct dma_fence *fence)
> -- 
> 2.26.3
> 

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