Re: [PATCH 05/10] drm/i915: skip DRM_I915_LOW_LEVEL_TRACEPOINTS with NOTRACE

[Steven Rostedt <rostedt@goodmis.org>]

On Wed, 10 Apr 2024 13:08:57 +0200
Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:

> On 2024-04-09 11:55:33 [-0400], Steven Rostedt wrote:
> > I believe you need to do it in the .c file:
> > 
> > Can you try something like this?
> >   
> …
> >  ?  
> 
> I tried and nothing changed because the lowlevel config option isn't the
> problem. What about I drop this and replace 4/10 from this series with
> the patch below? After enabling all tracing I don't see any events in
> events/i915.

I don't see anything wrong with this approach.

> 
> Sebastian
> 
> --------------------->8----------------------------  
> 
> From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Date: Thu, 6 Dec 2018 09:52:20 +0100
> Subject: [PATCH] drm/i915: Disable tracing points on PREEMPT_RT
> 
> 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 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.
> 
> Reported-by: Luca Abeni <lucabe72@gmail.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
>  drivers/gpu/drm/i915/display/intel_display_trace.h | 4 ++++
>  drivers/gpu/drm/i915/i915_trace.h                  | 4 ++++
>  2 files changed, 8 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_display_trace.h b/drivers/gpu/drm/i915/display/intel_display_trace.h
> index 7862e7cefe027..e4608d855bfba 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_trace.h
> +++ b/drivers/gpu/drm/i915/display/intel_display_trace.h
> @@ -9,6 +9,10 @@
>  #if !defined(__INTEL_DISPLAY_TRACE_H__) || defined(TRACE_HEADER_MULTI_READ)
>  #define __INTEL_DISPLAY_TRACE_H__
>  
> +#ifdef CONFIG_PREEMPT_RT

Hmm, should these be:

 #if defined(CONFIG_PREEMPT_RT) && !defined(NOTRACE)

?

because it's not protected due to the TRACE_HEADER_MULTI_READ.

-- Steve


> +#define NOTRACE
> +#endif
> +
>  #include <linux/string_helpers.h>
>  #include <linux/types.h>
>  #include <linux/tracepoint.h>
> diff --git a/drivers/gpu/drm/i915/i915_trace.h b/drivers/gpu/drm/i915/i915_trace.h
> index ce1cbee1b39dd..c54653cf72c95 100644
> --- a/drivers/gpu/drm/i915/i915_trace.h
> +++ b/drivers/gpu/drm/i915/i915_trace.h
> @@ -6,6 +6,10 @@
>  #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>