From 2a1195f0e085742ee91645203ac5f30fb3cad399 Mon Sep 17 00:00:00 2001 From: Daniel Bristot de Oliveira Date: Thu, 11 May 2023 18:32:01 +0200 Subject: [PATCH] tracing/timerlat: Always wakeup the timerlat thread 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@kernel.org Cc: Juri Lelli Cc: stable@vger.kernel.org Fixes: a955d7eac177 ("trace: Add timerlat tracer") Signed-off-by: Daniel Bristot de Oliveira Signed-off-by: Steven Rostedt (Google) Signed-off-by: Greg Kroah-Hartman --- kernel/trace/trace_osnoise.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c index 689361097bb0..26111b0ca1da 100644 --- a/kernel/trace/trace_osnoise.c +++ b/kernel/trace/trace_osnoise.c @@ -1595,6 +1595,8 @@ static enum hrtimer_restart timerlat_irq(struct hrtimer *timer) osnoise_stop_tracing(); notify_new_max_latency(diff); + wake_up_process(tlat->kthread); + return HRTIMER_NORESTART; } }