From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Thu, 6 Dec 2018 09:52:20 +0100
Subject: [PATCH] drm/i915: disable tracing on -RT
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git
Git-commit: da77ceac3d20f27310a07a7c346a4ee6b40d6c28
Patch-mainline: Queued in subsystem maintainer repository
References: SLE Realtime Extension

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_i915_pipe_update_start() among other events
use functions acquire spin locks. A few trace points use
intel_get_crtc_scanline(), others use ->get_vblank_counter() wich also
might acquire a sleeping lock.

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

Cc: stable-rt@vger.kernel.org
Reported-by: Luca Abeni <lucabe72@gmail.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Daniel Wagner <dwagner@suse.de>
---
 drivers/gpu/drm/i915/i915_trace.h |    4 ++++
 1 file changed, 4 insertions(+)

--- a/drivers/gpu/drm/i915/i915_trace.h
+++ b/drivers/gpu/drm/i915/i915_trace.h
@@ -2,6 +2,10 @@
 #if !defined(_I915_TRACE_H_) || defined(TRACE_HEADER_MULTI_READ)
 #define _I915_TRACE_H_
 
+#ifdef CONFIG_PREEMPT_RT
+#define NOTRACE
+#endif
+
 #include <linux/stringify.h>
 #include <linux/types.h>
 #include <linux/tracepoint.h>