Subject: Blktrace: bail out early if block debugfs is not configured

From: Liu Bo <[email-masked]>
Date: Fri, 29 Jun 2018 09:56:08 +0800

commit e1a413245a564683697a3d02ec197b72cf009b89 upstream.

Since @blk_debugfs_root couldn't be configured dynamically, we can
save a few memory allocation if it's not there.

Signed-off-by: Liu Bo <[email-masked]>
Signed-off-by: Jens Axboe <[email-masked]>
[bwh: Cherry-picked for 4.14 to ease backporting a later fix]
Signed-off-by: Ben Hutchings <[email-masked]>
---
 kernel/trace/blktrace.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index 987daf9cc6e5..38e0b97eede6 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -498,6 +498,9 @@ static int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
 	if (!buts->buf_size || !buts->buf_nr)
 		return -EINVAL;
 
+	if (!blk_debugfs_root)
+		return -ENOENT;
+
 	strncpy(buts->name, name, BLKTRACE_BDEV_SIZE);
 	buts->name[BLKTRACE_BDEV_SIZE - 1] = '\0';
 
@@ -532,9 +535,6 @@ static int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
 
 	ret = -ENOENT;
 
-	if (!blk_debugfs_root)
-		goto err;
-
 	dir = debugfs_lookup(buts->name, blk_debugfs_root);
 	if (!dir)
 		bt->dir = dir = debugfs_create_dir(buts->name, blk_debugfs_root);