[Intel-gfx] [PATCH 2/2] drm/i915: Don't dereference request if it may have been retired

[Chris Wilson]

This has count me out on countless occasions, when we retrieve a pointer
from the submission/execlists backend, it does not carry a reference to
the context or ring. Those are only pinned while the rquest is active,
so if we see the request is completed, it may be in the process of being
retired and those pointers defunct.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=110938
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/gt/intel_engine_cs.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_engine_cs.c b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
index 898692989313..7fd33e81c2d9 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
@@ -1311,12 +1311,13 @@ static void hexdump(struct drm_printer *m, const void *buf, size_t len)
 	}
 }
 
-static void intel_engine_print_registers(const struct intel_engine_cs *engine,
+static void intel_engine_print_registers(struct intel_engine_cs *engine,
 					 struct drm_printer *m)
 {
 	struct drm_i915_private *dev_priv = engine->i915;
 	const struct intel_engine_execlists * const execlists =
 		&engine->execlists;
+	unsigned long flags;
 	u64 addr;
 
 	if (engine->id == RCS0 && IS_GEN_RANGE(dev_priv, 4, 7))
@@ -1397,15 +1398,16 @@ static void intel_engine_print_registers(const struct intel_engine_cs *engine,
 				   idx, hws[idx * 2], hws[idx * 2 + 1]);
 		}
 
-		rcu_read_lock();
+		spin_lock_irqsave(&engine->active.lock, flags);
 		for (idx = 0; idx < execlists_num_ports(execlists); idx++) {
 			struct i915_request *rq;
 			unsigned int count;
+			char hdr[80];
 
 			rq = port_unpack(&execlists->port[idx], &count);
-			if (rq) {
-				char hdr[80];
-
+			if (!rq) {
+				drm_printf(m, "\t\tELSP[%d] idle\n", idx);
+			} else if (!i915_request_signaled(rq)) {
 				snprintf(hdr, sizeof(hdr),
 					 "\t\tELSP[%d] count=%d, ring:{start:%08x, hwsp:%08x, seqno:%08x}, rq: ",
 					 idx, count,
@@ -1414,11 +1416,11 @@ static void intel_engine_print_registers(const struct intel_engine_cs *engine,
 					 hwsp_seqno(rq));
 				print_request(m, rq, hdr);
 			} else {
-				drm_printf(m, "\t\tELSP[%d] idle\n", idx);
+				print_request(m, rq, "\t\tELSP[%d] rq: ");
 			}
 		}
 		drm_printf(m, "\t\tHW active? 0x%x\n", execlists->active);
-		rcu_read_unlock();
+		spin_unlock_irqrestore(&engine->active.lock, flags);
 	} else if (INTEL_GEN(dev_priv) > 6) {
 		drm_printf(m, "\tPP_DIR_BASE: 0x%08x\n",
 			   ENGINE_READ(engine, RING_PP_DIR_BASE));
-- 
2.20.1