linux-kernel - [PATCH vz9] trace/osnoise: fix event unhooking

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Date:   Tue, 28 Dec 2021 17:05:53 +0300
From:   Nikita Yushchenko <nikita.yushchenko@...tuozzo.com>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Daniel Bristot de Oliveira <bristot@...nel.org>,
        Ingo Molnar <mingo@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kernel@...nvz.org
Subject: [PATCH vz9] trace/osnoise: fix event unhooking

If start_per_cpu_kthreads() called from osnoise_workload_start() returns
error, event hooks are left in broken state: unhook_irq_events() called
but unhook_thread_events() and unhook_softirq_events() not called, and
trace_osnoise_callback_enabled flag not cleared.

On the next tracer enable, hooks get not installed due to
trace_osnoise_callback_enabled flag.

And on the further tracer disable an attempt to remove non-installed
hooks happened, hitting a WARN_ON_ONCE() in tracepoint_remove_func().

Fix the error path by adding the missing part of cleanup.
While at this, introduce osnoise_unhook_events() to avoid code
duplication between this error path and notmal tracer disable.

Fixes: bce29ac9ce0b ("trace: Add osnoise tracer")
Signed-off-by: Nikita Yushchenko <nikita.yushchenko@...tuozzo.com>
---
 kernel/trace/trace_osnoise.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index 7520d43aed55..aa6f26612ccc 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -2123,6 +2123,13 @@ static int osnoise_hook_events(void)
 	return -EINVAL;
 }

+static void osnoise_unhook_events(void)
+{
+	unhook_thread_events();
+	unhook_softirq_events();
+	unhook_irq_events();
+}
+
 /*
  * osnoise_workload_start - start the workload and hook to events
  */
@@ -2155,7 +2162,8 @@ static int osnoise_workload_start(void)

 	retval = start_per_cpu_kthreads();
 	if (retval) {
-		unhook_irq_events();
+		trace_osnoise_callback_enabled = false;
+		osnoise_unhook_events();
 		return retval;
 	}

@@ -2186,9 +2194,7 @@ static void osnoise_workload_stop(void)

 	stop_per_cpu_kthreads();

-	unhook_irq_events();
-	unhook_softirq_events();
-	unhook_thread_events();
+	osnoise_unhook_events();
 }

 static void osnoise_tracer_start(struct trace_array *tr)
-- 
2.30.2