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[SRU,S,6/9] UBUNTU: SAUCE: drm/i915/guc: Consider also RCU depth in busy loop.

Message ID 20260924122708.1076074-7-benjamin.wheeler@canonical.com
State New
Headers show
Series Add drm/i915 PREEMPT_RT support | expand

Commit Message

Benjamin Wheeler Sept. 24, 2026, 12:27 p.m. UTC 
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

BugLink: https://bugs.launchpad.net/bugs/2168432

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@redhat.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Benjamin Wheeler <benjamin.wheeler@canonical.com>
---
 drivers/gpu/drm/i915/gt/uc/intel_guc.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
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Patch

diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc.h b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
index 053780f562c1..b25fa8f4dc4b 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