Revert "Scm: Remove unnecessary pid & credential references in Unix socket's send and receive path"

This reverts commit 0856a304.

As requested by Eric Dumazet, it has various ref-counting
problems and has introduced regressions.  Eric will add
a more suitable version of this performance fix.
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/scm.h

@@ -53,14 +53,6 @@ static __inline__ void scm_set_cred(struct scm_cookie *scm,
 	cred_to_ucred(pid, cred, &scm->creds);
 }
 
-static __inline__ void scm_set_cred_noref(struct scm_cookie *scm,
-				    struct pid *pid, const struct cred *cred)
-{
-	scm->pid  = pid;
-	scm->cred = cred;
-	cred_to_ucred(pid, cred, &scm->creds);
-}
-
 static __inline__ void scm_destroy_cred(struct scm_cookie *scm)
 {
 	put_pid(scm->pid);
@@ -78,15 +70,6 @@ static __inline__ void scm_destroy(struct scm_cookie *scm)
 		__scm_destroy(scm);
 }
 
-static __inline__ void scm_release(struct scm_cookie *scm)
-{
-	/* keep ref on pid and cred */
-	scm->pid = NULL;
-	scm->cred = NULL;
-	if (scm->fp)
-		__scm_destroy(scm);
-}
-
 static __inline__ int scm_send(struct socket *sock, struct msghdr *msg,
 			       struct scm_cookie *scm)
 {
@@ -125,14 +108,15 @@ static __inline__ void scm_recv(struct socket *sock, struct msghdr *msg,
 	if (!msg->msg_control) {
 		if (test_bit(SOCK_PASSCRED, &sock->flags) || scm->fp)
 			msg->msg_flags |= MSG_CTRUNC;
-		if (scm && scm->fp)
-			__scm_destroy(scm);
+		scm_destroy(scm);
 		return;
 	}
 
 	if (test_bit(SOCK_PASSCRED, &sock->flags))
 		put_cmsg(msg, SOL_SOCKET, SCM_CREDENTIALS, sizeof(scm->creds), &scm->creds);
 
+	scm_destroy_cred(scm);
+
 	scm_passec(sock, msg, scm);
 
 	if (!scm->fp)

net/unix/af_unix.c

@@ -1378,17 +1378,11 @@ static int unix_attach_fds(struct scm_cookie *scm, struct sk_buff *skb)
 	return max_level;
 }
 
-static int unix_scm_to_skb(struct scm_cookie *scm, struct sk_buff *skb,
-			   bool send_fds, bool ref)
+static int unix_scm_to_skb(struct scm_cookie *scm, struct sk_buff *skb, bool send_fds)
 {
 	int err = 0;
-	if (ref) {
-		UNIXCB(skb).pid  = get_pid(scm->pid);
-		UNIXCB(skb).cred = get_cred(scm->cred);
-	} else {
-		UNIXCB(skb).pid  = scm->pid;
-		UNIXCB(skb).cred = scm->cred;
-	}
+	UNIXCB(skb).pid  = get_pid(scm->pid);
+	UNIXCB(skb).cred = get_cred(scm->cred);
 	UNIXCB(skb).fp = NULL;
 	if (scm->fp && send_fds)
 		err = unix_attach_fds(scm, skb);
@@ -1413,7 +1407,7 @@ static int unix_dgram_sendmsg(struct kiocb *kiocb, struct socket *sock,
 	int namelen = 0; /* fake GCC */
 	int err;
 	unsigned hash;
-	struct sk_buff *skb = NULL;
+	struct sk_buff *skb;
 	long timeo;
 	struct scm_cookie tmp_scm;
 	int max_level;
@@ -1454,7 +1448,7 @@ static int unix_dgram_sendmsg(struct kiocb *kiocb, struct socket *sock,
 	if (skb == NULL)
 		goto out;
 
-	err = unix_scm_to_skb(siocb->scm, skb, true, false);
+	err = unix_scm_to_skb(siocb->scm, skb, true);
 	if (err < 0)
 		goto out_free;
 	max_level = err + 1;
@@ -1550,7 +1544,7 @@ static int unix_dgram_sendmsg(struct kiocb *kiocb, struct socket *sock,
 	unix_state_unlock(other);
 	other->sk_data_ready(other, len);
 	sock_put(other);
-	scm_release(siocb->scm);
+	scm_destroy(siocb->scm);
 	return len;
 
 out_unlock:
@@ -1560,8 +1554,7 @@ static int unix_dgram_sendmsg(struct kiocb *kiocb, struct socket *sock,
 out:
 	if (other)
 		sock_put(other);
-	if (skb == NULL)
-		scm_destroy(siocb->scm);
+	scm_destroy(siocb->scm);
 	return err;
 }
 
@@ -1573,7 +1566,7 @@ static int unix_stream_sendmsg(struct kiocb *kiocb, struct socket *sock,
 	struct sock *sk = sock->sk;
 	struct sock *other = NULL;
 	int err, size;
-	struct sk_buff *skb = NULL;
+	struct sk_buff *skb;
 	int sent = 0;
 	struct scm_cookie tmp_scm;
 	bool fds_sent = false;
@@ -1638,11 +1631,11 @@ static int unix_stream_sendmsg(struct kiocb *kiocb, struct socket *sock,
 		size = min_t(int, size, skb_tailroom(skb));
 
 
-		/* Only send the fds and no ref to pid in the first buffer */
-		err = unix_scm_to_skb(siocb->scm, skb, !fds_sent, fds_sent);
+		/* Only send the fds in the first buffer */
+		err = unix_scm_to_skb(siocb->scm, skb, !fds_sent);
 		if (err < 0) {
 			kfree_skb(skb);
-			goto out;
+			goto out_err;
 		}
 		max_level = err + 1;
 		fds_sent = true;
@@ -1650,7 +1643,7 @@ static int unix_stream_sendmsg(struct kiocb *kiocb, struct socket *sock,
 		err = memcpy_fromiovec(skb_put(skb, size), msg->msg_iov, size);
 		if (err) {
 			kfree_skb(skb);
-			goto out;
+			goto out_err;
 		}
 
 		unix_state_lock(other);
@@ -1667,10 +1660,7 @@ static int unix_stream_sendmsg(struct kiocb *kiocb, struct socket *sock,
 		sent += size;
 	}
 
-	if (skb)
-		scm_release(siocb->scm);
-	else
-		scm_destroy(siocb->scm);
+	scm_destroy(siocb->scm);
 	siocb->scm = NULL;
 
 	return sent;
@@ -1683,9 +1673,7 @@ static int unix_stream_sendmsg(struct kiocb *kiocb, struct socket *sock,
 		send_sig(SIGPIPE, current, 0);
 	err = -EPIPE;
 out_err:
-	if (skb == NULL)
-		scm_destroy(siocb->scm);
-out:
+	scm_destroy(siocb->scm);
 	siocb->scm = NULL;
 	return sent ? : err;
 }
@@ -1789,7 +1777,7 @@ static int unix_dgram_recvmsg(struct kiocb *iocb, struct socket *sock,
 		siocb->scm = &tmp_scm;
 		memset(&tmp_scm, 0, sizeof(tmp_scm));
 	}
-	scm_set_cred_noref(siocb->scm, UNIXCB(skb).pid, UNIXCB(skb).cred);
+	scm_set_cred(siocb->scm, UNIXCB(skb).pid, UNIXCB(skb).cred);
 	unix_set_secdata(siocb->scm, skb);
 
 	if (!(flags & MSG_PEEK)) {
@@ -1951,8 +1939,7 @@ static int unix_stream_recvmsg(struct kiocb *iocb, struct socket *sock,
 			}
 		} else {
 			/* Copy credentials */
-			scm_set_cred_noref(siocb->scm, UNIXCB(skb).pid,
-					   UNIXCB(skb).cred);
+			scm_set_cred(siocb->scm, UNIXCB(skb).pid, UNIXCB(skb).cred);
 			check_creds = 1;
 		}