FAILED: patch "[PATCH] tracing: Fix potential deadlock in cpu hotplug with osnoise" failed to apply to 6.12-stable tree

PATCH New [email protected] 2 participants 3 messages Mar 29 – Mar 30

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Stable branch Tracing Tracing OS noise / latency tracers

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lore

[email protected]

author maintainer

2026-03-29 07:18 UTC #0 lore raw

The patch below does not apply to the 6.12-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-6.12.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 '2026032952-shredding-snorkel-3530@gregkh' --subject-prefix 'PATCH 6.12.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]>

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();

Sasha Levin

maintainer

2026-03-30 14:18 UTC #1 lore raw

PATCH 1/2 tracing: Switch trace_osnoise.c code over to use guard() and __free()

From: Steven Rostedt <[email protected]>

[ Upstream commit 930d2b32c0af6895ba4c6ca6404e7f7b6dc214ed ]

The osnoise_hotplug_workfn() grabs two mutexes and cpu_read_lock(). It has various gotos to handle unlocking them. Switch them over to guard() and let the compiler worry about it.

The osnoise_cpus_read() has a temporary mask_str allocated and there's some gotos to make sure it gets freed on error paths. Switch that over to __free() to let the compiler worry about it.

Cc Masami Hiramatsu <[email protected]>

Cc Mark Rutland <[email protected]>

Cc Mathieu Desnoyers <[email protected]>

Cc Andrew Morton <[email protected]>

Cc Peter Zijlstra <[email protected]>

Link https://lore.kernel.org/[email protected] open here

Signed-off-by Steven Rostedt (Google) <[email protected]>

Stable-dep-of: 1f9885732248 ("tracing: Fix potential deadlock in cpu hotplug with osnoise")

Signed-off-by Sasha Levin <[email protected]>

---
 kernel/trace/trace_osnoise.c | 40 ++++++++++++------------------------
 1 file changed, 13 insertions(+), 27 deletions(-)

kernel/trace/trace_osnoise.c +13 ~~-27~~

index 216247913980e..412ca1efa956e 100644
@@ -2099,26 +2099,21 @@ static void osnoise_hotplug_workfn(struct work_struct *dummy)
 {
 	unsigned int cpu = smp_processor_id();
 
-	mutex_lock(&trace_types_lock);
+	guard(mutex)(&trace_types_lock);
 
 	if (!osnoise_has_registered_instances())
-		goto out_unlock_trace;
+		return;
 
-	mutex_lock(&interface_lock);
-	cpus_read_lock();
+	guard(mutex)(&interface_lock);
+	guard(cpus_read_lock)();
 
 	if (!cpu_online(cpu))
-		goto out_unlock;
+		return;
+
 	if (!cpumask_test_cpu(cpu, &osnoise_cpumask))
-		goto out_unlock;
+		return;
 
 	start_kthread(cpu);
-
-out_unlock:
-	cpus_read_unlock();
-	mutex_unlock(&interface_lock);
-out_unlock_trace:
-	mutex_unlock(&trace_types_lock);
 }
 
 static DECLARE_WORK(osnoise_hotplug_work, osnoise_hotplug_workfn);

@@ -2316,31 +2311,22 @@ static ssize_t
 osnoise_cpus_read(struct file *filp, char __user *ubuf, size_t count,
 		  loff_t *ppos)
 {
-	char *mask_str;
+	char *mask_str __free(kfree) = NULL;
 	int len;
 
-	mutex_lock(&interface_lock);
+	guard(mutex)(&interface_lock);
 
 	len = snprintf(NULL, 0, "%*pbl\n", cpumask_pr_args(&osnoise_cpumask)) + 1;
 	mask_str = kmalloc(len, GFP_KERNEL);
-	if (!mask_str) {
-		count = -ENOMEM;
-		goto out_unlock;
-	}
+	if (!mask_str)
+		return -ENOMEM;
 
 	len = snprintf(mask_str, len, "%*pbl\n", cpumask_pr_args(&osnoise_cpumask));
-	if (len >= count) {
-		count = -EINVAL;
-		goto out_free;
-	}
+	if (len >= count)
+		return -EINVAL;
 
 	count = simple_read_from_buffer(ubuf, count, ppos, mask_str, len);
 
-out_free:
-	kfree(mask_str);
-out_unlock:
-	mutex_unlock(&interface_lock);
-
 	return count;
 }

Signature · 1 line

2.53.0

Sasha Levin

maintainer

2026-03-30 14:18 UTC #2 lore raw

PATCH 2/2 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]>

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]>

Signed-off-by Sasha Levin <[email protected]>

---
 kernel/trace/trace_osnoise.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

kernel/trace/trace_osnoise.c +5 -5

index 412ca1efa956e..7d96be13367f3 100644
@@ -2104,8 +2104,8 @@ 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;

@@ -2268,11 +2268,11 @@ 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;

@@ -2288,8 +2288,8 @@ 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();

@@ -2375,16 +2375,16 @@ 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();

Signature · 1 line

2.53.0