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Commit 04171313 authored by Chris Wilson's avatar Chris Wilson
Browse files

drm/i915: Always double check for a missed interrupt for new bottom halves 



After assigning ourselves as the new bottom-half, we must perform a
cursory check to prevent a missed interrupt.  Either we miss the interrupt
whilst programming the hardware, or if there was a previous waiter (for
a later seqno) they may be woken instead of us (due to the inherent race
in the unlocked read of b->tasklet in the irq handler) and so we miss the
wake up.

Spotted-by: default avatarTvrtko Ursulin <tvrtko.ursulin@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=96806


Fixes: 688e6c72 ("drm/i915: Slaughter the thundering... herd")
Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: default avatarTvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1467805142-22219-1-git-send-email-chris@chris-wilson.co.uk
parent 91c8a326

drivers/gpu/drm/i915/intel_breadcrumbs.c

+11 −5
Original line number Diff line number Diff line
@@ -65,7 +65,7 @@ static void irq_disable(struct intel_engine_cs *engine) 
	engine->irq_posted = false;

}



static bool __intel_breadcrumbs_enable_irq(struct intel_breadcrumbs *b)

static void __intel_breadcrumbs_enable_irq(struct intel_breadcrumbs *b)

{

	struct intel_engine_cs *engine =

		container_of(b, struct intel_engine_cs, breadcrumbs);
@@ -73,7 +73,7 @@ static bool __intel_breadcrumbs_enable_irq(struct intel_breadcrumbs *b) 


	assert_spin_locked(&b->lock);

	if (b->rpm_wakelock)

		return false;

		return;



	/* Since we are waiting on a request, the GPU should be busy

	 * and should have its own rpm reference. For completeness,
@@ -93,8 +93,6 @@ static bool __intel_breadcrumbs_enable_irq(struct intel_breadcrumbs *b) 
	if (!b->irq_enabled ||

	    test_bit(engine->id, &i915->gpu_error.missed_irq_rings))

		mod_timer(&b->fake_irq, jiffies + 1);



	return engine->irq_posted;

}



static void __intel_breadcrumbs_disable_irq(struct intel_breadcrumbs *b)
@@ -233,7 +231,15 @@ static bool __intel_engine_add_wait(struct intel_engine_cs *engine, 
		GEM_BUG_ON(rb_first(&b->waiters) != &wait->node);

		b->first_wait = wait;

		smp_store_mb(b->tasklet, wait->tsk);

		first = __intel_breadcrumbs_enable_irq(b);

		/* After assigning ourselves as the new bottom-half, we must

		 * perform a cursory check to prevent a missed interrupt.

		 * Either we miss the interrupt whilst programming the hardware,

		 * or if there was a previous waiter (for a later seqno) they

		 * may be woken instead of us (due to the inherent race

		 * in the unlocked read of b->tasklet in the irq handler) and

		 * so we miss the wake up.

		 */

		__intel_breadcrumbs_enable_irq(b);

	}

	GEM_BUG_ON(!b->tasklet);

	GEM_BUG_ON(!b->first_wait);