SUNRPC: Fix potential race in put_rpccred()

We have to be careful when we try to unhash the credential in
put_rpccred(), because we're not holding the credcache lock, so the call to
rpcauth_unhash_cred() may fail if someone else has looked the cred up, and
obtained a reference to it.
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

net/sunrpc/auth.c

@@ -455,7 +455,7 @@ put_rpccred(struct rpc_cred *cred)
 	}
 	if (test_bit(RPCAUTH_CRED_UPTODATE, &cred->cr_flags) == 0)
 		rpcauth_unhash_cred(cred);
-	else if (test_bit(RPCAUTH_CRED_HASHED, &cred->cr_flags) != 0) {
+	if (test_bit(RPCAUTH_CRED_HASHED, &cred->cr_flags) != 0) {
 		cred->cr_expire = jiffies;
 		list_add_tail(&cred->cr_lru, &cred_unused);
 		number_cred_unused++;