@@ -102,7 +102,7 @@ execlists_active(const struct intel_engine_execlists *execlists)
{
GEM_BUG_ON(execlists->active - execlists->inflight >
execlists_num_ports(execlists));
- return READ_ONCE(*execlists->active);
+ return *READ_ONCE(execlists->active);
}
static inline void
@@ -2186,15 +2186,15 @@ static void process_csb(struct intel_engine_cs *engine)
while (*execlists->active)
execlists_schedule_out(*execlists->active++);
+ set_timeslice(engine);
+
/* switch pending to inflight */
GEM_BUG_ON(!assert_pending_valid(execlists, "promote"));
- execlists->active =
- memcpy(execlists->inflight,
- execlists->pending,
- execlists_num_ports(execlists) *
- sizeof(*execlists->pending));
-
- set_timeslice(engine);
+ WRITE_ONCE(execlists->active,
+ memcpy(execlists->inflight,
+ execlists->pending,
+ execlists_num_ports(execlists) *
+ sizeof(*execlists->pending)));
WRITE_ONCE(execlists->pending[0], NULL);
} else {
Since we want to do a lockless read of the current active request, and that request is written to by process_csb also without serialisation, we need to instruct gcc to take care in reading the pointer itself. Otherwise, we have observed execlists_active() to report 0x40. [ 2400.760381] igt/para-4098 1..s. 2376479300us : process_csb: rcs0 cs-irq head=3, tail=4 [ 2400.760826] igt/para-4098 1..s. 2376479303us : process_csb: rcs0 csb[4]: status=0x00000001:0x00000000 [ 2400.761271] igt/para-4098 1..s. 2376479306us : trace_ports: rcs0: promote { b9c59:2622, b9c55:2624 } [ 2400.761726] igt/para-4097 0d... 2376479311us : __i915_schedule: rcs0: -2147483648->3, inflight:0000000000000040, rq:ffff888208c1e940 which is impossible! Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> --- drivers/gpu/drm/i915/gt/intel_engine.h | 2 +- drivers/gpu/drm/i915/gt/intel_lrc.c | 14 +++++++------- 2 files changed, 8 insertions(+), 8 deletions(-)