[PATCH 3/4] drm/i915/guc: Consider also RCU depth in busy loop.

[Maarten Lankhorst]

From: Sebastian Andrzej Siewior <bigeasy at linutronix.de>

intel_guc_send_busy_loop() looks at in_atomic() and irqs_disabled() to
decide if it should busy-spin while waiting or if it may sleep.
Both checks will report false on PREEMPT_RT if sleeping spinlocks are
acquired leading to RCU splats while the function sleeps.

Check also if RCU has been disabled.

Reported-by: John B. Wyatt IV <jwyatt at redhat.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy at linutronix.de>
Link: https://lore.kernel.org/r/20250714153954.629393-8-bigeasy@linutronix.de
Signed-off-by: Maarten Lankhorst <dev at lankhorst.se>
---
 drivers/gpu/drm/i915/gt/uc/intel_guc.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc.h b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
index 053780f562c1a..b25fa8f4dc4bd 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc.h
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
@@ -362,7 +362,7 @@ static inline int intel_guc_send_busy_loop(struct intel_guc *guc,
 {
 	int err;
 	unsigned int sleep_period_ms = 1;
-	bool not_atomic = !in_atomic() && !irqs_disabled();
+	bool not_atomic = !in_atomic() && !irqs_disabled() && !rcu_preempt_depth();
 
 	/*
 	 * FIXME: Have caller pass in if we are in an atomic context to avoid
-- 
2.45.2