NFS: Initialise verifiers for visible dentries in readdir and lookup

Ensure that the verifiers are initialised before calling
d_splice_alias() in both nfs_prime_dcache() and nfs_lookup().

Reported-by: Michael Stoler <michael.stoler@vastdata.com>
Fixes: a1147b8 ("NFS: Fix up directory verifier races")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

Author: Trond Myklebust

fs/nfs/dir.c

@@ -789,16 +789,17 @@ void nfs_prime_dcache(struct dentry *parent, struct nfs_entry *entry,
 		goto out;
 	}
 
+	nfs_set_verifier(dentry, dir_verifier);
 	inode = nfs_fhget(dentry->d_sb, entry->fh, entry->fattr);
 	alias = d_splice_alias(inode, dentry);
 	d_lookup_done(dentry);
 	if (alias) {
 		if (IS_ERR(alias))
 			goto out;
+		nfs_set_verifier(alias, dir_verifier);
 		dput(dentry);
 		dentry = alias;
 	}
-	nfs_set_verifier(dentry, dir_verifier);
 	trace_nfs_readdir_lookup(d_inode(parent), dentry, 0);
 out:
 	dput(dentry);
@@ -1994,13 +1995,14 @@ struct dentry *nfs_lookup(struct inode *dir, struct dentry * dentry, unsigned in
 	nfs_lookup_advise_force_readdirplus(dir, flags);
 
 no_entry:
+	nfs_set_verifier(dentry, dir_verifier);
 	res = d_splice_alias(inode, dentry);
 	if (res != NULL) {
 		if (IS_ERR(res))
 			goto out;
+		nfs_set_verifier(res, dir_verifier);
 		dentry = res;
 	}
-	nfs_set_verifier(dentry, dir_verifier);
 out:
 	trace_nfs_lookup_exit(dir, dentry, flags, PTR_ERR_OR_ZERO(res));
 	nfs_free_fattr(fattr);