When mkdir succeeds, v9fs_vfs_mkdir_dotl() and v9fs_vfs_mkdir() return
ERR_PTR(0) which is incorrect. They should return NULL instead for
success and ERR_PTR() only with negative error codes for failure.

Return NULL instead of passing to ERR_PTR while err is zero
Fixes smatch warnings:
  fs/9p/vfs_inode_dotl.c:420 v9fs_vfs_mkdir_dotl() warn: passing zero to 'ERR_PTR'
  fs/9p/vfs_inode.c:695 v9fs_vfs_mkdir() warn: passing zero to 'ERR_PTR'

This change does not alter the runtime behavior since ERR_PTR(0) and NULL
are equivalent. However, it improves code readability and silences static
analyzer warnings.

Fixes: 88d5baf69082 ("Change inode_operations.mkdir to return struct dentry *")
Suggested-by: David Laight <david.laight.linux@gmail.com>
Acked-by: Christian Schoenebeck <linux_oss@crudebyte.com>
Signed-off-by: Hongling Zeng <zenghongling@kylinos.cn>

---
change inv1:
- Add clarification in commit message that this is not a functional
  change, as suggested by Christian Schoenebeck.
- Add acked-by.
---
Changes in v2:
- Simplified v9fs_vfs_mkdir() implementation based on reviewer feedback
- Remove unnecessary 'err' variable and use ERR_CAST()
- Add suggested-by
---
 fs/9p/vfs_inode.c      | 19 ++++++-------------
 fs/9p/vfs_inode_dotl.c |  4 ++--
 2 files changed, 8 insertions(+), 15 deletions(-)

diff --git a/fs/9p/vfs_inode.c b/fs/9p/vfs_inode.c
index d1508b1fe109..d2692bc20b08 100644
--- a/fs/9p/vfs_inode.c
+++ b/fs/9p/vfs_inode.c
@@ -672,27 +672,20 @@ v9fs_vfs_create(struct mnt_idmap *idmap, struct inode *dir,
 static struct dentry *v9fs_vfs_mkdir(struct mnt_idmap *idmap, struct inode *dir,
 				     struct dentry *dentry, umode_t mode)
 {
-	int err;
 	u32 perm;
 	struct p9_fid *fid;
 	struct v9fs_session_info *v9ses;
 
 	p9_debug(P9_DEBUG_VFS, "name %pd\n", dentry);
-	err = 0;
 	v9ses = v9fs_inode2v9ses(dir);
 	perm = unixmode2p9mode(v9ses, mode | S_IFDIR);
 	fid = v9fs_create(v9ses, dir, dentry, NULL, perm, P9_OREAD);
-	if (IS_ERR(fid)) {
-		err = PTR_ERR(fid);
-		fid = NULL;
-	} else {
-		inc_nlink(dir);
-		v9fs_invalidate_inode_attr(dir);
-	}
-
-	if (fid)
-		p9_fid_put(fid);
-	return ERR_PTR(err);
+	if (IS_ERR(fid))
+		return ERR_CAST(fid);
+	inc_nlink(dir);
+	v9fs_invalidate_inode_attr(dir);
+	p9_fid_put(fid);
+	return NULL;
 }
 
 /**
diff --git a/fs/9p/vfs_inode_dotl.c b/fs/9p/vfs_inode_dotl.c
index 71796a89bcf4..83a52a85ce08 100644
--- a/fs/9p/vfs_inode_dotl.c
+++ b/fs/9p/vfs_inode_dotl.c
@@ -349,7 +349,7 @@ static struct dentry *v9fs_vfs_mkdir_dotl(struct mnt_idmap *idmap,
 					  struct inode *dir, struct dentry *dentry,
 					  umode_t omode)
 {
-	int err;
+	int err = 0;
 	struct v9fs_session_info *v9ses;
 	struct p9_fid *fid = NULL, *dfid = NULL;
 	kgid_t gid;
@@ -412,7 +412,7 @@ static struct dentry *v9fs_vfs_mkdir_dotl(struct mnt_idmap *idmap,
 	p9_fid_put(fid);
 	v9fs_put_acl(dacl, pacl);
 	p9_fid_put(dfid);
-	return ERR_PTR(err);
+	return err ? ERR_PTR(err) : NULL;
 }
 
 static int
-- 
2.25.1