From 0d68e8202f26bd9a254edc34d3100b30cb4e6b7f Mon Sep 17 00:00:00 2001
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Wed, 8 Sep 2021 17:18:00 +0200
Subject: [PATCH 28/63] drm/i915/gt: Queue and wait for the irq_work item.

Disabling interrupts and invoking the irq_work function directly breaks
on PREEMPT_RT.
PREEMPT_RT does not invoke all irq_work from hardirq context because
some of the user have spinlock_t locking in the callback function.
These locks are then turned into a sleeping locks which can not be
acquired with disabled interrupts.

Using irq_work_queue() has the benefit that the irqwork will be invoked
in the regular context. In general there is "no" delay between enqueuing
the callback and its invocation because the interrupt is raised right
away on architectures which support it (which includes x86).

Use irq_work_queue() + irq_work_sync() instead invoking the callback
directly.

Reported-by: Clark Williams <williams@redhat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
---
 drivers/gpu/drm/i915/gt/intel_breadcrumbs.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
index f2973cd1a8aa..aa77f8601b8a 100644
--- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
@@ -315,7 +315,12 @@ void __intel_breadcrumbs_park(struct intel_breadcrumbs *b)
 		return;
 
 	/* Kick the work once more to drain the signalers, and disarm the irq */
-	irq_work_queue(&b->irq_work);
+	irq_work_sync(&b->irq_work);
+	while (READ_ONCE(b->irq_armed) && !atomic_read(&b->active)) {
+		irq_work_queue(&b->irq_work);
+		cond_resched();
+		irq_work_sync(&b->irq_work);
+	}
 }
 
 void intel_breadcrumbs_free(struct kref *kref)
-- 
2.46.0

