From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Thu, 22 Mar 2018 07:35:32 +0000
Subject: drm/i915: Use full serialisation around engine->irq_posted
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Git-commit: 1c645bf4378f1539df57c6228f5c4957c130324a
Patch-mainline: v4.18-rc1
References: FATE#326289 FATE#326079 FATE#326049 FATE#322398 FATE#326166

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: Michał 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>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Jeff McGee <jeff.mcgee@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180322073533.5313-3-chris@chris-wilson.co.uk

Acked-by: Petr Tesarik <ptesarik@suse.com>
---
 drivers/gpu/drm/i915/i915_irq.c |    7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

--- 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_
 	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) {