[Intel-gfx] [PATCH 10/51] drm/i915/guc: Extend deregistration fence to schedule disable

Matthew Brost
2021-07-16T20:00:13Z

Extend the deregistration context fence to fence whne a GuC context has
scheduling disable pending.

v2:
(John H)
- Update comment why we check the pin count within spin lock

Cc: John Harrison <john.c.harrison@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: John Harrison <john.c.harrison@intel.com>
---
.../gpu/drm/i915/gt/uc/intel_guc_submission.c | 40 +++++++++++++++----
1 file changed, 33 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
index 5519c988a6ca..9dc1a256e185 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
@@ -922,7 +922,22 @@ static void guc_context_sched_disable(struct intel_context *ce)
goto unpin;

spin_lock_irqsave(&ce->guc_state.lock, flags);
+
+ /*
+ * We have to check if the context has been pinned again as another pin
+ * operation is allowed to pass this function. Checking the pin count,
+ * within ce->guc_state.lock, synchronizes this function with
+ * guc_request_alloc ensuring a request doesn't slip through the
+ * 'context_pending_disable' fence. Checking within the spin lock (can't
+ * sleep) ensures another process doesn't pin this context and generate
+ * a request before we set the 'context_pending_disable' flag here.
+ */
+ if (unlikely(atomic_add_unless(&ce->pin_count, -2, 2))) {
+ spin_unlock_irqrestore(&ce->guc_state.lock, flags);
+ return;
+ }
guc_id = prep_context_pending_disable(ce);
+
spin_unlock_irqrestore(&ce->guc_state.lock, flags);

with_intel_runtime_pm(runtime_pm, wakeref)
@@ -1127,19 +1142,22 @@ static int guc_request_alloc(struct i915_request *rq)
out:
/*
* We block all requests on this context if a G2H is pending for a
- * context deregistration as the GuC will fail a context registration
- * while this G2H is pending. Once a G2H returns, the fence is released
- * that is blocking these requests (see guc_signal_context_fence).
+ * schedule disable or context deregistration as the GuC will fail a
+ * schedule enable or context registration if either G2H is pending
+ * respectfully. Once a G2H returns, the fence is released that is
+ * blocking these requests (see guc_signal_context_fence).
*
- * We can safely check the below field outside of the lock as it isn't
- * possible for this field to transition from being clear to set but
+ * We can safely check the below fields outside of the lock as it isn't
+ * possible for these fields to transition from being clear to set but
* converse is possible, hence the need for the check within the lock.
*/
- if (likely(!context_wait_for_deregister_to_register(ce)))
+ if (likely(!context_wait_for_deregister_to_register(ce) &&
+ !context_pending_disable(ce)))
return 0;

spin_lock_irqsave(&ce->guc_state.lock, flags);
- if (context_wait_for_deregister_to_register(ce)) {
+ if (context_wait_for_deregister_to_register(ce) ||
+ context_pending_disable(ce)) {
i915_sw_fence_await(&rq->submit);

list_add_tail(&rq->guc_fence_link, &ce->guc_state.fences);
@@ -1488,10 +1506,18 @@ int intel_guc_sched_done_process_msg(struct intel_guc *guc,
if (context_pending_enable(ce)) {
clr_context_pending_enable(ce);
} else if (context_pending_disable(ce)) {
+ /*
+ * Unpin must be done before __guc_signal_context_fence,
+ * otherwise a race exists between the requests getting
+ * submitted + retired before this unpin completes resulting in
+ * the pin_count going to zero and the context still being
+ * enabled.
+ */
intel_context_sched_disable_unpin(ce);

spin_lock_irqsave(&ce->guc_state.lock, flags);
clr_context_pending_disable(ce);
+ __guc_signal_context_fence(ce);
spin_unlock_irqrestore(&ce->guc_state.lock, flags);
}

--
2.28.0