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FAILED: patch "[PATCH] tracing: Fix potential deadlock in cpu hotplug with osnoise" failed to apply to 5.15-stable tree

PATCH New [email protected] 2 participants 2 messages Mar 29 – Mar 30

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Stable branch Tracing Tracing OS noise / latency tracers
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author maintainer
#0 lore raw

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 1f9885732248d22f788e4992c739a98c88ab8a55
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026032954-repossess-ascension-613b@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

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

From 1f9885732248d22f788e4992c739a98c88ab8a55 Mon Sep 17 00:00:00 2001
From: Luo Haiyang <[email protected]>
Date: Thu, 26 Mar 2026 14:19:53 +0800
Subject: [PATCH] tracing: Fix potential deadlock in cpu hotplug with osnoise

The following sequence may leads deadlock in cpu hotplug:

    task1        task2        task3
    -----        -----        -----

mutex_lock(&interface_lock)

            [CPU GOING OFFLINE]

            cpus_write_lock();
            osnoise_cpu_die();
              kthread_stop(task3);
                wait_for_completion();

                      osnoise_sleep();
                        mutex_lock(&interface_lock);

cpus_read_lock();

[DEAD LOCK]

Fix by swap the order of cpus_read_lock() and mutex_lock(&interface_lock).

Cc [email protected]
Cc <[email protected]>
Cc <[email protected]>
Cc <[email protected]>
Cc <[email protected]>
Fixes bce29ac9ce0bb ("trace: Add osnoise tracer")
Link https://patch.msgid.link/[email protected] open here
Reviewed-by Masami Hiramatsu (Google) <[email protected]>
Signed-off-by Luo Haiyang <[email protected]>
Signed-off-by Steven Rostedt (Google) <[email protected]>
kernel/trace/trace_osnoise.c +5 -5
index dee610e465b9..be6cf0bb3c03 100644
@@ -2073,8 +2073,8 @@ static void osnoise_hotplug_workfn(struct work_struct *dummy)
 	if (!osnoise_has_registered_instances())
 		return;
 
-	guard(mutex)(&interface_lock);
 	guard(cpus_read_lock)();
+	guard(mutex)(&interface_lock);
 
 	if (!cpu_online(cpu))
 		return;

@@ -2237,11 +2237,11 @@ static ssize_t osnoise_options_write(struct file *filp, const char __user *ubuf,
 	if (running)
 		stop_per_cpu_kthreads();
 
-	mutex_lock(&interface_lock);
 	/*
 	 * avoid CPU hotplug operations that might read options.
 	 */
 	cpus_read_lock();
+	mutex_lock(&interface_lock);
 
 	retval = cnt;
 

@@ -2257,8 +2257,8 @@ static ssize_t osnoise_options_write(struct file *filp, const char __user *ubuf,
 			clear_bit(option, &osnoise_options);
 	}
 
-	cpus_read_unlock();
 	mutex_unlock(&interface_lock);
+	cpus_read_unlock();
 
 	if (running)
 		start_per_cpu_kthreads();

@@ -2345,16 +2345,16 @@ osnoise_cpus_write(struct file *filp, const char __user *ubuf, size_t count,
 	if (running)
 		stop_per_cpu_kthreads();
 
-	mutex_lock(&interface_lock);
 	/*
 	 * osnoise_cpumask is read by CPU hotplug operations.
 	 */
 	cpus_read_lock();
+	mutex_lock(&interface_lock);
 
 	cpumask_copy(&osnoise_cpumask, osnoise_cpumask_new);
 
-	cpus_read_unlock();
 	mutex_unlock(&interface_lock);
+	cpus_read_unlock();
 
 	if (running)
 		start_per_cpu_kthreads();
maintainer
#1 lore raw

PATCH 1/1 tracing: Fix potential deadlock in cpu hotplug with osnoise

From: Luo Haiyang <[email protected]>

[ Upstream commit 1f9885732248d22f788e4992c739a98c88ab8a55 ]

The following sequence may leads deadlock in cpu hotplug:

    task1        task2        task3
    -----        -----        -----

mutex_lock(&interface_lock)

            [CPU GOING OFFLINE]

            cpus_write_lock();
            osnoise_cpu_die();
              kthread_stop(task3);
                wait_for_completion();

                      osnoise_sleep();
                        mutex_lock(&interface_lock);

cpus_read_lock();

[DEAD LOCK]

Fix by swap the order of cpus_read_lock() and mutex_lock(&interface_lock).

Cc [email protected]
Cc <[email protected]>
Cc <[email protected]>
Cc <[email protected]>
Cc <[email protected]>
Fixes bce29ac9ce0bb ("trace: Add osnoise tracer")
Link https://patch.msgid.link/[email protected] open here
Reviewed-by Masami Hiramatsu (Google) <[email protected]>
Signed-off-by Luo Haiyang <[email protected]>
Signed-off-by Steven Rostedt (Google) <[email protected]>
[ adapted guard() macros to lock/unlock calls ]
Signed-off-by Sasha Levin <[email protected]>
---
 kernel/trace/trace_osnoise.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)
kernel/trace/trace_osnoise.c +4 -4
index 5959b1d4ee459..66061e77cc514 100644
@@ -1620,8 +1620,8 @@ static void osnoise_hotplug_workfn(struct work_struct *dummy)
 	if (!osnoise_busy)
 		goto out_unlock_trace;
 
-	mutex_lock(&interface_lock);
 	cpus_read_lock();
+	mutex_lock(&interface_lock);
 
 	if (!cpu_online(cpu))
 		goto out_unlock;

@@ -1634,8 +1634,8 @@ static void osnoise_hotplug_workfn(struct work_struct *dummy)
 	start_kthread(cpu);
 
 out_unlock:
-	cpus_read_unlock();
 	mutex_unlock(&interface_lock);
+	cpus_read_unlock();
 out_unlock_trace:
 	mutex_unlock(&trace_types_lock);
 }

@@ -1772,16 +1772,16 @@ osnoise_cpus_write(struct file *filp, const char __user *ubuf, size_t count,
 	if (running)
 		osnoise_tracer_stop(tr);
 
-	mutex_lock(&interface_lock);
 	/*
 	 * osnoise_cpumask is read by CPU hotplug operations.
 	 */
 	cpus_read_lock();
+	mutex_lock(&interface_lock);
 
 	cpumask_copy(&osnoise_cpumask, osnoise_cpumask_new);
 
-	cpus_read_unlock();
 	mutex_unlock(&interface_lock);
+	cpus_read_unlock();
 
 	if (running)
 		osnoise_tracer_start(tr);
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