[for-next][PATCH 3/5] ring-buffer: Clean up resize_disabled checks

[Steven Rostedt <rostedt@kernel.org>]

From: Vincent Donnefort <vdonnefort@google.com>

ring_buffer_subbuf_order_set() checks for resize_disabled twice under
the same buffer->mutex hold. Moreover, this check duplicates the logic
in ring_buffer_resize(). Create a common helper rb_resize_disabled() to
factor out this code.

Link: https://patch.msgid.link/20260916152813.105082-2-vdonnefort@google.com
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/trace/ring_buffer.c | 63 +++++++++++++++++---------------------
 1 file changed, 28 insertions(+), 35 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 1b148cd891c8..15e3b9938e0f 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -3282,6 +3282,21 @@ static void update_pages_handler(struct work_struct *work)
 	complete(&cpu_buffer->update_done);
 }
 
+static bool rb_resize_disabled(struct trace_buffer *buffer, int cpu)
+{
+	lockdep_assert_held(&buffer->mutex);
+
+	if (cpu != RING_BUFFER_ALL_CPUS)
+		return atomic_read(&buffer->buffers[cpu]->resize_disabled);
+
+	for_each_buffer_cpu(buffer, cpu) {
+		if (atomic_read(&buffer->buffers[cpu]->resize_disabled))
+			return true;
+	}
+
+	return false;
+}
+
 /**
  * ring_buffer_resize - resize the ring buffer
  * @buffer: the buffer to resize.
@@ -3322,20 +3337,17 @@ int ring_buffer_resize(struct trace_buffer *buffer, unsigned long size,
 
 	nr_pages = rb_calculate_nr_pages(buffer, size);
 
-	if (cpu_id == RING_BUFFER_ALL_CPUS) {
-		/*
-		 * Don't succeed if resizing is disabled, as a reader might be
-		 * manipulating the ring buffer and is expecting a sane state while
-		 * this is true.
-		 */
-		for_each_buffer_cpu(buffer, cpu) {
-			cpu_buffer = buffer->buffers[cpu];
-			if (atomic_read(&cpu_buffer->resize_disabled)) {
-				err = -EBUSY;
-				goto out_err_unlock;
-			}
-		}
+	/*
+	 * Don't succeed if resizing is disabled, as a reader might be
+	 * manipulating the ring buffer and is expecting a sane state while
+	 * this is true.
+	 */
+	if (rb_resize_disabled(buffer, cpu_id)) {
+		err = -EBUSY;
+		goto out_err_unlock;
+	}
 
+	if (cpu_id == RING_BUFFER_ALL_CPUS) {
 		/* calculate the pages to update */
 		for_each_buffer_cpu(buffer, cpu) {
 			cpu_buffer = buffer->buffers[cpu];
@@ -3407,16 +3419,6 @@ int ring_buffer_resize(struct trace_buffer *buffer, unsigned long size,
 		if (nr_pages == cpu_buffer->nr_pages)
 			goto out;
 
-		/*
-		 * Don't succeed if resizing is disabled, as a reader might be
-		 * manipulating the ring buffer and is expecting a sane state while
-		 * this is true.
-		 */
-		if (atomic_read(&cpu_buffer->resize_disabled)) {
-			err = -EBUSY;
-			goto out_err_unlock;
-		}
-
 		cpu_buffer->nr_pages_to_update = nr_pages -
 						cpu_buffer->nr_pages;
 
@@ -7471,13 +7473,9 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order)
 
 	old_capacity = rb_subbuf_capacity(buffer);
 
-	/* The mmap fast path reads subbuf_order without buffer->mutex. */
-	for_each_buffer_cpu(buffer, cpu) {
-		if (!cpumask_test_cpu(cpu, buffer->cpumask))
-			continue;
-		if (atomic_read(&buffer->buffers[cpu]->resize_disabled))
-			return -EBUSY;
-	}
+	/* Check it is resizable before we touch subbuf_order */
+	if (rb_resize_disabled(buffer, RING_BUFFER_ALL_CPUS))
+		return -EBUSY;
 
 	atomic_inc(&buffer->record_disabled);
 
@@ -7494,11 +7492,6 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order)
 
 		cpu_buffer = buffer->buffers[cpu];
 
-		if (atomic_read(&cpu_buffer->resize_disabled)) {
-			err = -EBUSY;
-			goto error;
-		}
-
 		/* Update the number of pages to match the new size */
 		nr_pages = rb_calculate_nr_pages(buffer,
 						 old_capacity * buffer->buffers[cpu]->nr_pages);
-- 
2.53.0