Re: [RFC PATCH 1/2] sched/tracing: Don't re-read p->state when emitting sched_switch event

[Steven Rostedt]

On Mon, 29 Nov 2021 12:36:00 +0000
Valentin Schneider <valentin.schneider@xxxxxxx> wrote:

> As of commit
> 
>   c6e7bd7afaeb ("sched/core: Optimize ttwu() spinning on p->on_cpu")
> 
> the following sequence becomes possible:
> 
> 		      p->__state = TASK_INTERRUPTIBLE;
> 		      __schedule()
> 			deactivate_task(p);
>   ttwu()
>     READ !p->on_rq
>     p->__state=TASK_WAKING
> 			trace_sched_switch()
> 			  __trace_sched_switch_state()
> 			    task_state_index()
> 			      return 0;
> 
> TASK_WAKING isn't in TASK_REPORT, so the task appears as TASK_RUNNING in
> the trace event.
> 
> Prevent this by pushing the value read from __schedule() down the trace
> event.
> 
> Reported-by: Abhijeet Dharmapurikar <adharmap@xxxxxxxxxxx>
> Signed-off-by: Valentin Schneider <valentin.schneider@xxxxxxx>
> ---
>  include/linux/sched.h             | 11 ++++++++---
>  include/trace/events/sched.h      | 11 +++++++----
>  kernel/sched/core.c               |  4 ++--
>  kernel/trace/fgraph.c             |  4 +++-
>  kernel/trace/ftrace.c             |  4 +++-
>  kernel/trace/trace_events.c       |  8 ++++++--
>  kernel/trace/trace_sched_switch.c |  1 +

I believe you may have missed some functions that register the sched_switch
event. Do a git grep on register_trace_sched_switch.

-- Steve


>  7 files changed, 30 insertions(+), 13 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index d2e261adb8ea..d00837d12b9d 100644