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

This reverts commit 0856a304091b33a8e8f9f9c98e776f425af2b625.

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>

1 files changed, 16 insertions, 29 deletions

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index e6d9d1014ed..ec68e1c05b8 100644
--- a/net/unix/af_unix.c
+++ b/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 @@ restart:
         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 @@ out_free:
 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 @@ pipe_err:
                 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;
                 }