From: Daniel Bristot de Oliveira bristot@kernel.org
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/1ed8f830638b20a39d535d27d908e319a...
Cc: Juri Lelli juri.lelli@redhat.com Cc: stable@vger.kernel.org Fixes: a955d7eac177 ("trace: Add timerlat tracer") Signed-off-by: Daniel Bristot de Oliveira bristot@kernel.org Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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; } }