From fcae496153a3ce719082746a01c81dd581e7a239 Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Fri, 8 May 2020 10:29:27 +0100 Subject: [PATCH] drm/i915: Prevent using semaphores to chain up to external fences The downside of using semaphores is that we lose metadata passing along the signaling chain. This is particularly nasty when we need to pass along a fatal error such as EFAULT or EDEADLK. For fatal errors we want to scrub the request before it is executed, which means that we cannot preload the request onto HW and have it wait upon a semaphore. Signed-off-by: Chris Wilson Reviewed-by: Mika Kuoppala Link: https://patchwork.freedesktop.org/patch/msgid/20200508092933.738-3-chris@chris-wilson.co.uk --- drivers/gpu/drm/i915/i915_request.c | 26 +++++++++++++++++++++ drivers/gpu/drm/i915/i915_scheduler_types.h | 1 + 2 files changed, 27 insertions(+) diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c index 9df2cb8d66d03..2c0de3a3b8e8a 100644 --- a/drivers/gpu/drm/i915/i915_request.c +++ b/drivers/gpu/drm/i915/i915_request.c @@ -1003,6 +1003,15 @@ emit_semaphore_wait(struct i915_request *to, if (!rcu_access_pointer(from->hwsp_cacheline)) goto await_fence; + /* + * If this or its dependents are waiting on an external fence + * that may fail catastrophically, then we want to avoid using + * sempahores as they bypass the fence signaling metadata, and we + * lose the fence->error propagation. + */ + if (from->sched.flags & I915_SCHED_HAS_EXTERNAL_CHAIN) + goto await_fence; + /* Just emit the first semaphore we see as request space is limited. */ if (already_busywaiting(to) & mask) goto await_fence; @@ -1065,12 +1074,29 @@ i915_request_await_request(struct i915_request *to, struct i915_request *from) return ret; } + if (from->sched.flags & I915_SCHED_HAS_EXTERNAL_CHAIN) + to->sched.flags |= I915_SCHED_HAS_EXTERNAL_CHAIN; + return 0; } +static void mark_external(struct i915_request *rq) +{ + /* + * The downside of using semaphores is that we lose metadata passing + * along the signaling chain. This is particularly nasty when we + * need to pass along a fatal error such as EFAULT or EDEADLK. For + * fatal errors we want to scrub the request before it is executed, + * which means that we cannot preload the request onto HW and have + * it wait upon a semaphore. + */ + rq->sched.flags |= I915_SCHED_HAS_EXTERNAL_CHAIN; +} + static int __i915_request_await_external(struct i915_request *rq, struct dma_fence *fence) { + mark_external(rq); return i915_sw_fence_await_dma_fence(&rq->submit, fence, fence->context ? I915_FENCE_TIMEOUT : 0, I915_FENCE_GFP); diff --git a/drivers/gpu/drm/i915/i915_scheduler_types.h b/drivers/gpu/drm/i915/i915_scheduler_types.h index 7186875088a0a..6ab2c5289bed3 100644 --- a/drivers/gpu/drm/i915/i915_scheduler_types.h +++ b/drivers/gpu/drm/i915/i915_scheduler_types.h @@ -66,6 +66,7 @@ struct i915_sched_node { struct i915_sched_attr attr; unsigned int flags; #define I915_SCHED_HAS_SEMAPHORE_CHAIN BIT(0) +#define I915_SCHED_HAS_EXTERNAL_CHAIN BIT(1) intel_engine_mask_t semaphores; }; -- 2.39.5