Re: [PATCH] ring-buffer: fix error handling in ring_buffer_subbuf_order_set()
From: Steven Rostedt <rostedt@goodmis.org>
Date: 2025-06-06 10:51:19
On Fri, 6 Jun 2025 12:12:17 +0300 Dmitry Antipov [off-list ref] wrote:
quoted hunk ↗ jump to hunk
In 'ring_buffer_subbuf_order_set()', enlarge critical section to ensure that error handling takes place with per-buffer mutex hold, thus preventing list corruption and other concurrency-related issues. Reported-by: syzbot+05d673e83ec640f0ced9@syzkaller.appspotmail.com 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 <redacted> --- kernel/trace/ring_buffer.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index e24509bd0af5..2028a24d6418 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c@@ -6908,9 +6908,6 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order) buffer->subbuf_order = old_order; buffer->subbuf_size = old_size; - atomic_dec(&buffer->record_disabled);
There's no reason to move the record_disable. Enabling recording here is fine, as the pages being freed have not been added to the ring buffer.
quoted hunk ↗ jump to hunk
- mutex_unlock(&buffer->mutex); - for_each_buffer_cpu(buffer, cpu) { cpu_buffer = buffer->buffers[cpu];@@ -6923,6 +6920,9 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order) } } + atomic_dec(&buffer->record_disabled); + mutex_unlock(&buffer->mutex);
As this moves the mutex to the end, we can instead just remove the mutex_unlock()s and replace the mutex() with: guard(mutex)(&buffer->mutex); Care to send a v2? -- Steve
+ return err; } EXPORT_SYMBOL_GPL(ring_buffer_subbuf_order_set);