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* [CI 1/2] drm/i915: Disable tracepoints for PREEMPT_RT
@ 2025-10-03 14:40 Maarten Lankhorst
  2025-10-03 14:40 ` [CI 2/2] drm/i915/display: Make intel_crtc_get_vblank_counter safe on PREEMPT_RT Maarten Lankhorst
                   ` (2 more replies)
  0 siblings, 3 replies; 4+ messages in thread
From: Maarten Lankhorst @ 2025-10-03 14:40 UTC (permalink / raw)
  To: intel-gfx
  Cc: intel-xe, Maarten Lankhorst, Tvrtko Ursulin, Luca Abeni,
	Steven Rostedt, Sebastian Andrzej Siewior, Jani Nikula

Luca Abeni reported this:
| BUG: scheduling while atomic: kworker/u8:2/15203/0x00000003
| CPU: 1 PID: 15203 Comm: kworker/u8:2 Not tainted 4.19.1-rt3 #10
| Call Trace:
|  rt_spin_lock+0x3f/0x50
|  gen6_read32+0x45/0x1d0 [i915]
|  g4x_get_vblank_counter+0x36/0x40 [i915]
|  trace_event_raw_event_i915_pipe_update_start+0x7d/0xf0 [i915]

The tracing events use trace_intel_pipe_update_start() among other events
use functions acquire spinlock_t locks which are transformed into
sleeping locks on PREEMPT_RT. A few trace points use
intel_get_crtc_scanline(), others use ->get_vblank_counter() wich also
might acquire a sleeping locks on PREEMPT_RT.
At the time the arguments are evaluated within trace point, preemption
is disabled and so the locks must not be acquired on PREEMPT_RT.

Based on this I don't see any other way than disable trace points on
PREMPT_RT.

[mlankhorst]
The original patch was insufficient, and since the tracing
infrastructure does not allow for partial disabling of tracepoints.

Completely disable tracing for the entire i915 driver in PREEMPT_RT,
a separate fix for display tracepoints on xe is added to make those
work.

Cc: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Reported-by: Luca Abeni <lucabe72@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Co-developed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Link: https://lore.kernel.org/r/20250828090944.101069-1-dev@lankhorst.se
Signed-off-by: Maarten Lankhorst <dev@lankhorst.se>
---
 drivers/gpu/drm/i915/Makefile | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
index 78a45a6681df3..6d7800e25e554 100644
--- a/drivers/gpu/drm/i915/Makefile
+++ b/drivers/gpu/drm/i915/Makefile
@@ -13,6 +13,11 @@ subdir-ccflags-$(CONFIG_DRM_I915_WERROR) += -Werror
 # drivers. Define I915 when building i915.
 subdir-ccflags-y += -DI915
 
+# FIXME: Disable tracepoints on i915 for PREEMPT_RT, unfortunately
+# it's an all or nothing flag. You cannot selectively disable
+# only some tracepoints.
+subdir-ccflags-$(CONFIG_PREEMPT_RT) += -DNOTRACE
+
 subdir-ccflags-y += -I$(src)
 
 # Please keep these build lists sorted!
-- 
2.51.0


^ permalink raw reply related	[flat|nested] 4+ messages in thread

end of thread, other threads:[~2025-10-04  6:47 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2025-10-03 14:40 [CI 1/2] drm/i915: Disable tracepoints for PREEMPT_RT Maarten Lankhorst
2025-10-03 14:40 ` [CI 2/2] drm/i915/display: Make intel_crtc_get_vblank_counter safe on PREEMPT_RT Maarten Lankhorst
2025-10-03 15:54 ` ✓ i915.CI.BAT: success for series starting with [CI,1/2] drm/i915: Disable tracepoints for PREEMPT_RT Patchwork
2025-10-04  6:47 ` ✗ i915.CI.Full: failure " Patchwork

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