On Thu, 22 Aug 2024 08:20:52 -0300
"Luis Claudio R. Goncalves" [off-list ref] wrote:

You mean the 

+	if (!tlat_var->kthread) {
+		/* the fd has been closed already */

bit or the kthread handling in rtla itself?

As Tomas already said, thank you for testing and reviewing the suggested fix!

The close only happens once, but the kthread does get freed elsewhere.

I used my new persistent ring buffer to debug this! I'll be posting some
more patches that allow trace_printk() and friends to use the persistent
ring buffer (or any instance) soon.

For this bug, I would recommend instead doing:

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index 66a871553d4a..53de719f35cb 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c

@@ -2579,7 +2587,8 @@ static int timerlat_fd_release(struct inode *inode, struct file *file)
 	osn_var = per_cpu_ptr(&per_cpu_osnoise_var, cpu);
 	tlat_var = per_cpu_ptr(&per_cpu_timerlat_var, cpu);
 
-	hrtimer_cancel(&tlat_var->timer);
+	if (tlat_var->kthread)
+		hrtimer_cancel(&tlat_var->timer);
 	memset(tlat_var, 0, sizeof(*tlat_var));
 
 	osn_var->sampling = 0;

-- Steve