[PATCH v2] vfs: Pre-allocate superblock in sget_fc() if !test

[Waiman Long]

When the test function is not defined in sget_fc(), we always need
to allocate a new superblock. So there is no point in acquiring the
sb_lock twice in this case. Optimize the !test case by pre-allocating
the superblock first before acquring the lock.

Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
---
 fs/super.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/super.c b/fs/super.c
index a6405d44d4ca..6601267f6fe0 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -520,6 +520,8 @@ struct super_block *sget_fc(struct fs_context *fc,
 	struct user_namespace *user_ns = fc->global ? &init_user_ns : fc->user_ns;
 	int err;
 
+	if (!test)
+		goto prealloc;
 retry:
 	spin_lock(&sb_lock);
 	if (test) {
@@ -530,6 +532,7 @@ struct super_block *sget_fc(struct fs_context *fc,
 	}
 	if (!s) {
 		spin_unlock(&sb_lock);
+prealloc:
 		s = alloc_super(fc->fs_type, fc->sb_flags, user_ns);
 		if (!s)
 			return ERR_PTR(-ENOMEM);
-- 
2.27.0