nfsd: fix end_creating() conversion

Avoid a double-unlock as nfs_create_locked() will have unlocked the
parent and do the dput() manually.

Christian Brauner <brauner@kernel.org> says:

I've taken Neil's proposed fix from [1] and added a commit message.

Fixes: https://lore.kernel.org/202511252132.2c621407-lkp@intel.com [1]
Fixes: bd6ede8 ("VFS/nfsd/cachefiles/ovl: introduce start_removing() and end_removing()")
Signed-off-by: Neil Brown <neil@brown.name>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: neilbrown

fs/nfsd/nfsproc.c

@@ -407,6 +407,9 @@ nfsd_proc_create(struct svc_rqst *rqstp)
 		/* File doesn't exist. Create it and set attrs */
 		resp->status = nfsd_create_locked(rqstp, dirfhp, &attrs, type,
 						  rdev, newfhp);
+		/* nfsd_create_locked() unlocked the parent */
+		dput(dchild);
+		goto out_write;
 	} else if (type == S_IFREG) {
 		dprintk("nfsd:   existing %s, valid=%x, size=%ld\n",
 			argp->name, attr->ia_valid, (long) attr->ia_size);

fs/nfsd/vfs.c

@@ -1633,16 +1633,14 @@ nfsd_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
 		return nfserrno(host_err);
 
 	err = fh_compose(resfhp, fhp->fh_export, dchild, fhp);
-	/*
-	 * We unconditionally drop our ref to dchild as fh_compose will have
-	 * already grabbed its own ref for it.
-	 */
 	if (err)
 		goto out_unlock;
 	err = fh_fill_pre_attrs(fhp);
 	if (err != nfs_ok)
 		goto out_unlock;
 	err = nfsd_create_locked(rqstp, fhp, attrs, type, rdev, resfhp);
+	/* nfsd_create_locked() unlocked the parent */
+	dput(dchild);
 	return err;
 
 out_unlock: