From: Sebastian Andrzej Siewior Date: Tue, 3 Oct 2023 21:37:21 +0200 Subject: [PATCH 7/8] drm/i915/guc: Consider also RCU depth in busy loop. Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.11/older/patches-6.11-rt7.tar.xz 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" Reviewed-by: Rodrigo Vivi Signed-off-by: Sebastian Andrzej Siewior --- drivers/gpu/drm/i915/gt/uc/intel_guc.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- 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_lo { 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