diff options
| -rw-r--r-- | drivers/gpu/drm/i915/gt/intel_lrc.c | 15 | ||||
| -rw-r--r-- | drivers/gpu/drm/i915/i915_request.c | 25 |
2 files changed, 34 insertions, 6 deletions
diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c index 24322ef08aa4..9eeaca957a7e 100644 --- a/drivers/gpu/drm/i915/gt/intel_lrc.c +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c @@ -2060,6 +2060,14 @@ static inline void clear_ports(struct i915_request **ports, int count) memset_p((void **)ports, NULL, count); } +static inline void +copy_ports(struct i915_request **dst, struct i915_request **src, int count) +{ + /* A memcpy_p() would be very useful here! */ + while (count--) + WRITE_ONCE(*dst++, *src++); /* avoid write tearing */ +} + static void execlists_dequeue(struct intel_engine_cs *engine) { struct intel_engine_execlists * const execlists = &engine->execlists; @@ -2648,10 +2656,9 @@ static void process_csb(struct intel_engine_cs *engine) /* switch pending to inflight */ GEM_BUG_ON(!assert_pending_valid(execlists, "promote")); - memcpy(execlists->inflight, - execlists->pending, - execlists_num_ports(execlists) * - sizeof(*execlists->pending)); + copy_ports(execlists->inflight, + execlists->pending, + execlists_num_ports(execlists)); smp_wmb(); /* complete the seqlock */ WRITE_ONCE(execlists->active, execlists->inflight); diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c index 0b2fe55e6194..781a6783affe 100644 --- a/drivers/gpu/drm/i915/i915_request.c +++ b/drivers/gpu/drm/i915/i915_request.c @@ -388,17 +388,38 @@ static bool __request_in_flight(const struct i915_request *signal) * As we know that there are always preemption points between * requests, we know that only the currently executing request * may be still active even though we have cleared the flag. - * However, we can't rely on our tracking of ELSP[0] to known + * However, we can't rely on our tracking of ELSP[0] to know * which request is currently active and so maybe stuck, as * the tracking maybe an event behind. Instead assume that * if the context is still inflight, then it is still active * even if the active flag has been cleared. + * + * To further complicate matters, if there a pending promotion, the HW + * may either perform a context switch to the second inflight execlists, + * or it may switch to the pending set of execlists. In the case of the + * latter, it may send the ACK and we process the event copying the + * pending[] over top of inflight[], _overwriting_ our *active. Since + * this implies the HW is arbitrating and not struck in *active, we do + * not worry about complete accuracy, but we do require no read/write + * tearing of the pointer [the read of the pointer must be valid, even + * as the array is being overwritten, for which we require the writes + * to avoid tearing.] + * + * Note that the read of *execlists->active may race with the promotion + * of execlists->pending[] to execlists->inflight[], overwritting + * the value at *execlists->active. This is fine. The promotion implies + * that we received an ACK from the HW, and so the context is not + * stuck -- if we do not see ourselves in *active, the inflight status + * is valid. If instead we see ourselves being copied into *active, + * we are inflight and may signal the callback. */ if (!intel_context_inflight(signal->context)) return false; rcu_read_lock(); - for (port = __engine_active(signal->engine); (rq = *port); port++) { + for (port = __engine_active(signal->engine); + (rq = READ_ONCE(*port)); /* may race with promotion of pending[] */ + port++) { if (rq->context == signal->context) { inflight = i915_seqno_passed(rq->fence.seqno, signal->fence.seqno); |