diff mbox

drm/i915: Use full serialisation around engine->irq_posted

Message ID 20180321191533.4385-1-chris@chris-wilson.co.uk (mailing list archive)
State New, archived
Headers show

Commit Message

Chris Wilson March 21, 2018, 7:15 p.m. UTC
Using engine->irq_posted for execlists, we are not always serialised by
the tasklet as we supposed. On the reset paths, the tasklet is disabled
and ignored. Instead, we manipulate the engine->irq_posted directly to
account for the reset, but if an interrupt fired before the reset and so
wrote to engine->irq_posted, that write may not be flushed from the
local CPU's cacheline until much later as the tasklet is already active
and so does not generate a mb(). To correctly serialise the interrupt
with reset, we need serialisation on the set_bit() itself.

And at last Mika can be happy.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: MichaƂ Winiarski <michal.winiarski@intel.com>
CC: Michel Thierry <michel.thierry@intel.com>
Cc: Jeff McGee <jeff.mcgee@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
---
 drivers/gpu/drm/i915/i915_irq.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)
diff mbox

Patch

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index fa7310766217..27aee25429b7 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -1405,10 +1405,9 @@  gen8_cs_irq_handler(struct intel_engine_cs *engine, u32 iir)
 	bool tasklet = false;
 
 	if (iir & GT_CONTEXT_SWITCH_INTERRUPT) {
-		if (READ_ONCE(engine->execlists.active)) {
-			__set_bit(ENGINE_IRQ_EXECLIST, &engine->irq_posted);
-			tasklet = true;
-		}
+		if (READ_ONCE(engine->execlists.active))
+			tasklet = !test_and_set_bit(ENGINE_IRQ_EXECLIST,
+						    &engine->irq_posted);
 	}
 
 	if (iir & GT_RENDER_USER_INTERRUPT) {