FAILED: patch "[PATCH] trace/hwlat: Do not start per-cpu thread if it is already" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 08697bca9bbba15f2058fdbd9f970bd5f6a8a2e8
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '[email protected]' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

08697bca9bbb ("trace/hwlat: Do not start per-cpu thread if it is already running") ff78f6679d2e ("trace/hwlat: make use of the helper function kthread_run_on_cpu()")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 08697bca9bbba15f2058fdbd9f970bd5f6a8a2e8 Mon Sep 17 00:00:00 2001
From: Tero Kristo <[email protected]>
Date: Fri, 10 Mar 2023 12:04:51 +0200
Subject: [PATCH] trace/hwlat: Do not start per-cpu thread if it is already
running

The hwlatd tracer will end up starting multiple per-cpu threads with the following script:

#!/bin/sh
cd /sys/kernel/debug/tracing
echo 0 > tracing_on
echo hwlat > current_tracer
echo per-cpu > hwlat_detector/mode
echo 100000 > hwlat_detector/width
echo 200000 > hwlat_detector/window
echo 1 > tracing_on

To fix the issue, check if the hwlatd thread for the cpu is already running, before starting a new one. Along with the previous patch, this avoids running multiple instances of the same CPU thread on the system.

index edc26dc22c3f..c4945f8adc11 100644
@@ -492,6 +492,10 @@ static int start_cpu_kthread(unsigned int cpu)
 {
 	struct task_struct *kthread;
 
+	/* Do not start a new hwlatd thread if it is already running */
+	if (per_cpu(hwlat_per_cpu_data, cpu).kthread)
+		return 0;
+
 	kthread = kthread_run_on_cpu(kthread_fn, NULL, cpu, "hwlatd/%u");
 	if (IS_ERR(kthread)) {
 		pr_err(BANNER "could not start sampling thread\n");