FAILED: patch "[PATCH] tracing/timerlat: Fix duplicated kthread creation due to CPU" failed to apply to 6.1-stable tree

The patch below does not apply to the 6.1-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-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x 0bb0a5c12ecf36ad561542bbb95f96355e036a02
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2024100741-afoot-canal-db89@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..

Possible dependencies:

0bb0a5c12ecf ("tracing/timerlat: Fix duplicated kthread creation due to CPU online/offline") 177e1cc2f412 ("tracing/osnoise: Use a cpumask to know what threads are kthreads") e88ed227f639 ("tracing/timerlat: Add user-space interface")
4998e7fda149 ("tracing/osnoise: Switch from PF_NO_SETAFFINITY to migrate_disable") 30838fcd8107 ("tracing/osnoise: Add OSNOISE_WORKLOAD option")
b179d48b6aab ("tracing/osnoise: Add osnoise/options file")

thanks,

greg k-h

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

From 0bb0a5c12ecf36ad561542bbb95f96355e036a02 Mon Sep 17 00:00:00 2001
From: Wei Li <[email protected]>
Date: Tue, 24 Sep 2024 17:45:11 +0800
Subject: [PATCH] tracing/timerlat: Fix duplicated kthread creation due to CPU
online/offline

osnoise_hotplug_workfn() is the asynchronous online callback for "trace/osnoise:online". It may be congested when a CPU goes online and offline repeatedly and is invoked for multiple times after a certain online.

This will lead to kthread leak and timer corruption. Add a check in start_kthread() to prevent this situation.

index 1439064f65d6..d1a539913a5f 100644
@@ -2007,6 +2007,10 @@ static int start_kthread(unsigned int cpu)
 	void *main = osnoise_main;
 	char comm[24];
 
+	/* Do not start a new thread if it is already running */
+	if (per_cpu(per_cpu_osnoise_var, cpu).kthread)
+		return 0;
+
 	if (timerlat_enabled()) {
 		snprintf(comm, 24, "timerlat/%d", cpu);
 		main = timerlat_main;

@@ -2061,11 +2065,10 @@ static int start_per_cpu_kthreads(void)
 		if (cpumask_test_and_clear_cpu(cpu, &kthread_cpumask)) {
 			struct task_struct *kthread;
 
-			kthread = per_cpu(per_cpu_osnoise_var, cpu).kthread;
+			kthread = xchg_relaxed(&(per_cpu(per_cpu_osnoise_var, cpu).kthread), NULL);
 			if (!WARN_ON(!kthread))
 				kthread_stop(kthread);
 		}
-		per_cpu(per_cpu_osnoise_var, cpu).kthread = NULL;
 	}
 
 	for_each_cpu(cpu, current_mask) {