vfio/virtio: Use guard() for list_lock where applicable

Convert list_lock mutex acquisitions to use guard() and scoped_guard()
where the lock scope aligns with the function or block scope.  This
simplifies virtiovf_get_data_buff_from_pos() by replacing goto-based
unwinding with direct returns.

Assisted-by: Claude:claude-opus-4-6
Signed-off-by: Alex Williamson <alex.williamson@nvidia.com>
Reviewed-by: Yishai Hadas <yishaih@nvidia.com>
Link: https://lore.kernel.org/r/20260414200625.3601509-3-alex.williamson@nvidia.com
Signed-off-by: Alex Williamson <alex@shazbot.org>

Author: Alex Williamson

drivers/vfio/pci/virtio/migrate.c

@@ -142,9 +142,8 @@ virtiovf_alloc_data_buffer(struct virtiovf_migration_file *migf, size_t length)
 
 static void virtiovf_put_data_buffer(struct virtiovf_data_buffer *buf)
 {
-	mutex_lock(&buf->migf->list_lock);
+	guard(mutex)(&buf->migf->list_lock);
 	list_add_tail(&buf->buf_elm, &buf->migf->avail_list);
-	mutex_unlock(&buf->migf->list_lock);
 }
 
 static int
@@ -306,32 +305,27 @@ virtiovf_get_data_buff_from_pos(struct virtiovf_migration_file *migf,
 				loff_t pos, bool *end_of_data)
 {
 	struct virtiovf_data_buffer *buf;
-	bool found = false;
 
 	*end_of_data = false;
-	mutex_lock(&migf->list_lock);
+	guard(mutex)(&migf->list_lock);
+
 	if (list_empty(&migf->buf_list)) {
 		*end_of_data = true;
-		goto end;
+		return NULL;
 	}
 
 	buf = list_first_entry(&migf->buf_list, struct virtiovf_data_buffer,
 			       buf_elm);
 	if (pos >= buf->start_pos &&
-	    pos < buf->start_pos + buf->length) {
-		found = true;
-		goto end;
-	}
+	    pos < buf->start_pos + buf->length)
+		return buf;
 
 	/*
 	 * As we use a stream based FD we may expect having the data always
 	 * on first chunk
 	 */
 	migf->state = VIRTIOVF_MIGF_STATE_ERROR;
-
-end:
-	mutex_unlock(&migf->list_lock);
-	return found ? buf : NULL;
+	return NULL;
 }
 
 static ssize_t virtiovf_buf_read(struct virtiovf_data_buffer *vhca_buf,
@@ -370,10 +364,9 @@ static ssize_t virtiovf_buf_read(struct virtiovf_data_buffer *vhca_buf,
 	}
 
 	if (*pos >= vhca_buf->start_pos + vhca_buf->length) {
-		mutex_lock(&vhca_buf->migf->list_lock);
+		guard(mutex)(&vhca_buf->migf->list_lock);
 		list_del_init(&vhca_buf->buf_elm);
 		list_add_tail(&vhca_buf->buf_elm, &vhca_buf->migf->avail_list);
-		mutex_unlock(&vhca_buf->migf->list_lock);
 	}
 
 	return done;
@@ -550,9 +543,10 @@ virtiovf_add_buf_header(struct virtiovf_data_buffer *header_buf,
 	header_buf->length = sizeof(header);
 	header_buf->start_pos = header_buf->migf->max_pos;
 	migf->max_pos += header_buf->length;
-	mutex_lock(&migf->list_lock);
-	list_add_tail(&header_buf->buf_elm, &migf->buf_list);
-	mutex_unlock(&migf->list_lock);
+
+	scoped_guard(mutex, &migf->list_lock)
+		list_add_tail(&header_buf->buf_elm, &migf->buf_list);
+
 	return 0;
 }
 
@@ -617,9 +611,10 @@ virtiovf_read_device_context_chunk(struct virtiovf_migration_file *migf,
 
 	buf->start_pos = buf->migf->max_pos;
 	migf->max_pos += buf->length;
-	mutex_lock(&migf->list_lock);
-	list_add_tail(&buf->buf_elm, &migf->buf_list);
-	mutex_unlock(&migf->list_lock);
+
+	scoped_guard(mutex, &migf->list_lock)
+		list_add_tail(&buf->buf_elm, &migf->buf_list);
+
 	return 0;
 
 out_header: