FAILED: patch "[PATCH] tracing: Fix potential deadlock in cpu hotplug with osnoise" failed to apply to 6.6-stable tree

FAILED: patch "[PATCH] tracing: Fix potential deadlock in cpu hotplug with osnoise" failed to apply to 6.6-stable tree

[gregkh]

The patch below does not apply to the 6.6-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 <stable@vger.kernel.org>.

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-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 1f9885732248d22f788e4992c739a98c88ab8a55
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026032953-garnet-dropout-ed0f@gregkh' --subject-prefix 'PATCH 6.6.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 <luo.haiyang@zte.com.cn>
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: stable@vger.kernel.org
Cc: <mathieu.desnoyers@efficios.com>
Cc: <zhang.run@zte.com.cn>
Cc: <yang.tao172@zte.com.cn>
Cc: <ran.xiaokai@zte.com.cn>
Fixes: bce29ac9ce0bb ("trace: Add osnoise tracer")
Link: https://patch.msgid.link/20260326141953414bVSj33dAYktqp9Oiyizq8@zte.com.cn
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Luo Haiyang <luo.haiyang@zte.com.cn>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index dee610e465b9..be6cf0bb3c03 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -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();

[PATCH 6.6.y 1/2] tracing: Switch trace_osnoise.c code over to use guard() and __free()

[Sasha Levin]

From: Steven Rostedt <rostedt@goodmis.org>

[ 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 <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/20241225222931.517329690@goodmis.org
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Stable-dep-of: 1f9885732248 ("tracing: Fix potential deadlock in cpu hotplug with osnoise")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/trace/trace_osnoise.c | 40 ++++++++++++------------------------
 1 file changed, 13 insertions(+), 27 deletions(-)

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index 4d12d02965a4b..6bf8d18a15b7c 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -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;
 }
 
-- 
2.53.0

[PATCH 6.6.y 2/2] tracing: Fix potential deadlock in cpu hotplug with osnoise

[Sasha Levin]

From: Luo Haiyang <luo.haiyang@zte.com.cn>

[ 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: stable@vger.kernel.org
Cc: <mathieu.desnoyers@efficios.com>
Cc: <zhang.run@zte.com.cn>
Cc: <yang.tao172@zte.com.cn>
Cc: <ran.xiaokai@zte.com.cn>
Fixes: bce29ac9ce0bb ("trace: Add osnoise tracer")
Link: https://patch.msgid.link/20260326141953414bVSj33dAYktqp9Oiyizq8@zte.com.cn
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Luo Haiyang <luo.haiyang@zte.com.cn>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/trace/trace_osnoise.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index 6bf8d18a15b7c..3b039374c993e 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -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();
-- 
2.53.0