From: Al Viro <viro@zeniv.linux.org.uk>
Date: Wed, 10 Feb 2021 22:13:03 -0500
Subject: [PATCH] cifs: have ->mkdir() handle race with another client sanely
Git-commit: 3bcb39b086bf8d7c3cff013564f86162ec497d90
References: bsc#1190317
Patch-mainline: v5.12-rc3

if we have mkdir request reported successful *and* simulating lookup
gets us a non-directory (which is possible if another client has
managed to get rmdir and create in between), the sane action is not
to mangle ->i_mode of non-directory inode to S_IFDIR | mode, it's
"report success and return with dentry negative unhashed" - that
way the next lookup will do the right thing.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Acked-by: Enzo Matsumiya <ematsumiya@suse.de>
---
 fs/cifs/inode.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/fs/cifs/inode.c b/fs/cifs/inode.c
index d46b36d52211..80c487fcf10e 100644
--- a/fs/cifs/inode.c
+++ b/fs/cifs/inode.c
@@ -1739,6 +1739,16 @@ cifs_mkdir_qinfo(struct inode *parent, struct dentry *dentry, umode_t mode,
 	if (rc)
 		return rc;
 
+	if (!S_ISDIR(inode->i_mode)) {
+		/*
+		 * mkdir succeeded, but another client has managed to remove the
+		 * sucker and replace it with non-directory.  Return success,
+		 * but don't leave the child in dcache.
+		 */
+		 iput(inode);
+		 d_drop(dentry);
+		 return 0;
+	}
 	/*
 	 * setting nlink not necessary except in cases where we failed to get it
 	 * from the server or was set bogus. Also, since this is a brand new
@@ -1790,7 +1800,7 @@ cifs_mkdir_qinfo(struct inode *parent, struct dentry *dentry, umode_t mode,
 		}
 	}
 	d_instantiate(dentry, inode);
-	return rc;
+	return 0;
 }
 
 static int
-- 
2.33.0