[for-linus][PATCH 2/3] ring-buffer: Fix buffer locking in ring_buffer_subbuf_order_set()

[Steven Rostedt]

From: Dmitry Antipov <dmantipov@xxxxxxxxx>

Enlarge the critical section in ring_buffer_subbuf_order_set() to
ensure that error handling takes place with per-buffer mutex held,
thus preventing list corruption and other concurrency-related issues.

Cc: stable@xxxxxxxxxxxxxxx
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Tzvetomir Stoyanov <tz.stoyanov@xxxxxxxxx>
Link: https://lore.kernel.org/20250606112242.1510605-1-dmantipov@xxxxxxxxx
Reported-by: syzbot+05d673e83ec640f0ced9@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=05d673e83ec640f0ced9
Fixes: f9b94daa542a8 ("ring-buffer: Set new size of the ring buffer sub page")
Signed-off-by: Dmitry Antipov <dmantipov@xxxxxxxxx>
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
---
 kernel/trace/ring_buffer.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index e24509bd0af5..00fc38d70e86 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -6795,7 +6795,7 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order)
 	old_size = buffer->subbuf_size;
 
 	/* prevent another thread from changing buffer sizes */
-	mutex_lock(&buffer->mutex);
+	guard(mutex)(&buffer->mutex);
 	atomic_inc(&buffer->record_disabled);
 
 	/* Make sure all commits have finished */
@@ -6900,7 +6900,6 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order)
 	}
 
 	atomic_dec(&buffer->record_disabled);
-	mutex_unlock(&buffer->mutex);
 
 	return 0;
 
@@ -6909,7 +6908,6 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order)
 	buffer->subbuf_size = old_size;
 
 	atomic_dec(&buffer->record_disabled);
-	mutex_unlock(&buffer->mutex);
 
 	for_each_buffer_cpu(buffer, cpu) {
 		cpu_buffer = buffer->buffers[cpu];
-- 
2.47.2