Re: [PATCH 5/6] drm/i915: Wrap engine->schedule in RCU locks for set-wedge protection

Mika Kuoppala
2018-03-09T13:55:31Z

Chris Wilson <chris@chris-wilson.co.uk> writes:

> Similar to the staging around handling of engine->submit_request, we
> need to stop adding to the execlists->queue prior to calling
> engine->cancel_requests. cancel_requests will move requests from the
> queue onto the timeline, so if we add a request onto the queue after that
> point, it will be lost.
>
> Fixes: af7a8ffad9c5 ("drm/i915: Use rcu instead of stop_machine in set_wedged")
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Mika Kuoppala <mika.kuoppala@intel.com>

Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>

> ---
> drivers/gpu/drm/i915/i915_gem.c | 13 +++++++------
> drivers/gpu/drm/i915/i915_request.c | 2 ++
> 2 files changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 30cd07ebcb8e..3b44952e089f 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -471,10 +471,11 @@ static void __fence_set_priority(struct dma_fence *fence, int prio)
>
> rq = to_request(fence);
> engine = rq->engine;
> - if (!engine->schedule)
> - return;
>
> - engine->schedule(rq, prio);
> + rcu_read_lock();
> + if (engine->schedule)
> + engine->schedule(rq, prio);
> + rcu_read_unlock();
> }
>
> static void fence_set_priority(struct dma_fence *fence, int prio)
> @@ -3214,8 +3215,11 @@ void i915_gem_set_wedged(struct drm_i915_private *i915)
> */
> for_each_engine(engine, i915, id) {
> i915_gem_reset_prepare_engine(engine);
> +
> engine->submit_request = nop_submit_request;
> + engine->schedule = NULL;
> }
> + i915->caps.scheduler = 0;
>
> /*
> * Make sure no one is running the old callback before we proceed with
> @@ -3233,11 +3237,8 @@ void i915_gem_set_wedged(struct drm_i915_private *i915)
> * start to complete all requests.
> */
> engine->submit_request = nop_complete_submit_request;
> - engine->schedule = NULL;
> }
>
> - i915->caps.scheduler = 0;
> -
> /*
> * Make sure no request can slip through without getting completed by
> * either this call here to intel_engine_init_global_seqno, or the one
> diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
> index 69b378a323fc..0258449579f8 100644
> --- a/drivers/gpu/drm/i915/i915_request.c
> +++ b/drivers/gpu/drm/i915/i915_request.c
> @@ -1082,8 +1082,10 @@ void __i915_request_add(struct i915_request *request, bool flush_caches)
> * decide whether to preempt the entire chain so that it is ready to
> * run at the earliest possible convenience.
> */
> + rcu_read_lock();
> if (engine->schedule)
> engine->schedule(request, request->ctx->priority);
> + rcu_read_unlock();
>
> local_bh_disable();
> i915_sw_fence_commit(&request->submit);
> --
> 2.16.2
>
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