This is a note to let you know that I've just added the patch titled
tracing/timerlat: Always wakeup the timerlat thread
to the 6.3-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
tracing-timerlat-always-wakeup-the-timerlat-thread.patch
and it can be found in the queue-6.3 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 632478a05821bc1c9b55c3a1dd0fb1be7bfa1acc Mon Sep 17 00:00:00 2001
From: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
Date: Thu, 11 May 2023 18:32:01 +0200
Subject: tracing/timerlat: Always wakeup the timerlat thread
From: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
commit 632478a05821bc1c9b55c3a1dd0fb1be7bfa1acc upstream.
While testing rtla timerlat auto analysis, I reach a condition where
the interface was not receiving tracing data. I was able to manually
reproduce the problem with these steps:
# echo 0 > tracing_on # disable trace
# echo 1 > osnoise/stop_tracing_us # stop trace if timerlat irq > 1 us
# echo timerlat > current_tracer # enable timerlat tracer
# sleep 1 # wait... that is the time when rtla
# apply configs like prio or cgroup
# echo 1 > tracing_on # start tracing
# cat trace
# tracer: timerlat
#
# _-----=> irqs-off
# / _----=> need-resched
# | / _---=> hardirq/softirq
# || / _--=> preempt-depth
# ||| / _-=> migrate-disable
# |||| / delay
# ||||| ACTIVATION
# TASK-PID CPU# ||||| TIMESTAMP ID CONTEXT LATENCY
# | | | ||||| | | | |
NOTHING!
Then, trying to enable tracing again with echo 1 > tracing_on resulted
in no change: the trace was still not tracing.
This problem happens because the timerlat IRQ hits the stop tracing
condition while tracing is off, and do not wake up the timerlat thread,
so the timerlat threads are kept sleeping forever, resulting in no
trace, even after re-enabling the tracer.
Avoid this condition by always waking up the threads, even after stopping
tracing, allowing the tracer to return to its normal operating after
a new tracing on.
Link: https://lore.kernel.org/linux-trace-kernel/1ed8f830638b20a39d535d27d908e319a9a3c4e2.1683822622.git.bristot@xxxxxxxxxx
Cc: Juri Lelli <juri.lelli@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Fixes: a955d7eac177 ("trace: Add timerlat tracer")
Signed-off-by: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/trace/trace_osnoise.c | 2 ++
1 file changed, 2 insertions(+)
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -1652,6 +1652,8 @@ static enum hrtimer_restart timerlat_irq
osnoise_stop_tracing();
notify_new_max_latency(diff);
+ wake_up_process(tlat->kthread);
+
return HRTIMER_NORESTART;
}
}
Patches currently in stable-queue which might be from bristot@xxxxxxxxxx are
queue-6.3/tracing-timerlat-always-wakeup-the-timerlat-thread.patch
