linux-kernel - [PATCH 2/3] tracing/timerlat: Print stacktrace in the IRQ handler if needed

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Date:   Tue, 10 May 2022 11:45:24 +0200
From:   Daniel Bristot de Oliveira <bristot@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
        linux-trace-devel@...r.kernel.org
Cc:     Daniel Bristot de Oliveira <bristot@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Clark Williams <williams@...hat.com>
Subject: [PATCH 2/3] tracing/timerlat: Print stacktrace in the IRQ handler if needed

If print_stack and stop_tracing_us are set, and stop_tracing_us is hit
with latency higher than or equal to print_stack, print the
stack at the IRQ handler as it is useful to define the root cause for
the IRQ latency.

Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Ingo Molnar <mingo@...hat.com>
Signed-off-by: Daniel Bristot de Oliveira <bristot@...nel.org>
---
 Documentation/trace/timerlat-tracer.rst |  5 +++--
 kernel/trace/trace_osnoise.c            | 13 +++++++++++++
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/Documentation/trace/timerlat-tracer.rst b/Documentation/trace/timerlat-tracer.rst
index 64d1fe6e9b93..d643c95c01eb 100644
--- a/Documentation/trace/timerlat-tracer.rst
+++ b/Documentation/trace/timerlat-tracer.rst
@@ -74,8 +74,9 @@ directory. The timerlat configs are:
  - stop_tracing_total_us: stop the system tracing if a
    timer latency at the *thread* context is higher than the configured
    value happens. Writing 0 disables this option.
- - print_stack: save the stack of the IRQ occurrence, and print
-   it after the *thread context* event".
+ - print_stack: save the stack of the IRQ occurrence. The stack is printed
+   after the *thread context* event, or at the IRQ handler if *stop_tracing_us*
+   is hit.
 
 timerlat and osnoise
 ----------------------------
diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index 6494ca27ea6f..9b204ee3c6f5 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -1580,6 +1580,19 @@ static enum hrtimer_restart timerlat_irq(struct hrtimer *timer)
 
 	if (osnoise_data.stop_tracing) {
 		if (time_to_us(diff) >= osnoise_data.stop_tracing) {
+
+			/*
+			 * At this point, if stop_tracing is set and <= print_stack,
+			 * print_stack is set and would be printed in the thread handler.
+			 *
+			 * Thus, print the stack trace as it is helpful to define the
+			 * root cause of an IRQ latency.
+			 */
+			if (osnoise_data.stop_tracing <= osnoise_data.print_stack) {
+				timerlat_save_stack(0);
+				timerlat_dump_stack(time_to_us(diff));
+			}
+
 			osnoise_stop_tracing();
 			notify_new_max_latency(diff);
 		}
-- 
2.32.0