net/smc: rebuild nonblocking connect

The recent poll change may lead to stalls for non-blocking connecting
SMC sockets, since sock_poll_wait is no longer performed on the
internal CLC socket, but on the outer SMC socket.  kernel_connect() on
the internal CLC socket returns with -EINPROGRESS, but the wake up
logic does not work in all cases. If the internal CLC socket is still
in state TCP_SYN_SENT when polled, sock_poll_wait() from sock_poll()
does not sleep. It is supposed to sleep till the state of the internal
CLC socket switches to TCP_ESTABLISHED.

This problem triggered a redesign of the SMC nonblocking connect logic.
This patch introduces a connect worker covering all connect steps
followed by a wake up of socket waiters. It allows to get rid of all
delays and locks in smc_poll().

Fixes: c0129a061442 ("smc: convert to ->poll_mask")
Signed-off-by: Ursula Braun <ubraun@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 71 insertions, 28 deletions

diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index da7f02edcd37..4d1d4ddb2f49 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c
@@ -45,6 +45,7 @@ static DEFINE_MUTEX(smc_create_lgr_pending);	/* serialize link group
                                                  */
 
 static void smc_tcp_listen_work(struct work_struct *);
+static void smc_connect_work(struct work_struct *);
 
 static void smc_set_keepalive(struct sock *sk, int val)
 {
@@ -122,6 +123,12 @@ static int smc_release(struct socket *sock)
                 goto out;
 
         smc = smc_sk(sk);
+
+        /* cleanup for a dangling non-blocking connect */
+        flush_work(&smc->connect_work);
+        kfree(smc->connect_info);
+        smc->connect_info = NULL;
+
         if (sk->sk_state == SMC_LISTEN)
                 /* smc_close_non_accepted() is called and acquires
                  * sock lock for child sockets again
@@ -186,6 +193,7 @@ static struct sock *smc_sock_alloc(struct net *net, struct socket *sock,
         sk->sk_protocol = protocol;
         smc = smc_sk(sk);
         INIT_WORK(&smc->tcp_listen_work, smc_tcp_listen_work);
+        INIT_WORK(&smc->connect_work, smc_connect_work);
         INIT_DELAYED_WORK(&smc->conn.tx_work, smc_tx_work);
         INIT_LIST_HEAD(&smc->accept_q);
         spin_lock_init(&smc->accept_q_lock);
@@ -576,6 +584,35 @@ static int __smc_connect(struct smc_sock *smc)
         return 0;
 }
 
+static void smc_connect_work(struct work_struct *work)
+{
+        struct smc_sock *smc = container_of(work, struct smc_sock,
+                                            connect_work);
+        int rc;
+
+        lock_sock(&smc->sk);
+        rc = kernel_connect(smc->clcsock, &smc->connect_info->addr,
+                            smc->connect_info->alen, smc->connect_info->flags);
+        if (smc->clcsock->sk->sk_err) {
+                smc->sk.sk_err = smc->clcsock->sk->sk_err;
+                goto out;
+        }
+        if (rc < 0) {
+                smc->sk.sk_err = -rc;
+                goto out;
+        }
+
+        rc = __smc_connect(smc);
+        if (rc < 0)
+                smc->sk.sk_err = -rc;
+
+out:
+        smc->sk.sk_state_change(&smc->sk);
+        kfree(smc->connect_info);
+        smc->connect_info = NULL;
+        release_sock(&smc->sk);
+}
+
 static int smc_connect(struct socket *sock, struct sockaddr *addr,
                        int alen, int flags)
 {
@@ -605,15 +642,32 @@ static int smc_connect(struct socket *sock, struct sockaddr *addr,
 
         smc_copy_sock_settings_to_clc(smc);
         tcp_sk(smc->clcsock->sk)->syn_smc = 1;
-        rc = kernel_connect(smc->clcsock, addr, alen, flags);
-        if (rc)
-                goto out;
+        if (flags & O_NONBLOCK) {
+                if (smc->connect_info) {
+                        rc = -EALREADY;
+                        goto out;
+                }
+                smc->connect_info = kzalloc(alen + 2 * sizeof(int), GFP_KERNEL);
+                if (!smc->connect_info) {
+                        rc = -ENOMEM;
+                        goto out;
+                }
+                smc->connect_info->alen = alen;
+                smc->connect_info->flags = flags ^ O_NONBLOCK;
+                memcpy(&smc->connect_info->addr, addr, alen);
+                schedule_work(&smc->connect_work);
+                rc = -EINPROGRESS;
+        } else {
+                rc = kernel_connect(smc->clcsock, addr, alen, flags);
+                if (rc)
+                        goto out;
 
-        rc = __smc_connect(smc);
-        if (rc < 0)
-                goto out;
-        else
-                rc = 0; /* success cases including fallback */
+                rc = __smc_connect(smc);
+                if (rc < 0)
+                        goto out;
+                else
+                        rc = 0; /* success cases including fallback */
+        }
 
 out:
         release_sock(sk);
@@ -1278,34 +1332,17 @@ static __poll_t smc_poll_mask(struct socket *sock, __poll_t events)
         struct sock *sk = sock->sk;
         __poll_t mask = 0;
         struct smc_sock *smc;
-        int rc;
 
         if (!sk)
                 return EPOLLNVAL;
 
         smc = smc_sk(sock->sk);
-        sock_hold(sk);
-        lock_sock(sk);
         if ((sk->sk_state == SMC_INIT) || smc->use_fallback) {
                 /* delegate to CLC child sock */
-                release_sock(sk);
                 mask = smc->clcsock->ops->poll_mask(smc->clcsock, events);
-                lock_sock(sk);
                 sk->sk_err = smc->clcsock->sk->sk_err;
-                if (sk->sk_err) {
+                if (sk->sk_err)
                         mask |= EPOLLERR;
-                } else {
-                        /* if non-blocking connect finished ... */
-                        if (sk->sk_state == SMC_INIT &&
-                            mask & EPOLLOUT &&
-                            smc->clcsock->sk->sk_state != TCP_CLOSE) {
-                                rc = __smc_connect(smc);
-                                if (rc < 0)
-                                        mask |= EPOLLERR;
-                                /* success cases including fallback */
-                                mask |= EPOLLOUT | EPOLLWRNORM;
-                        }
-                }
         } else {
                 if (sk->sk_err)
                         mask |= EPOLLERR;
@@ -1334,8 +1371,6 @@ static __poll_t smc_poll_mask(struct socket *sock, __poll_t events)
                         mask |= EPOLLPRI;
 
         }
-        release_sock(sk);
-        sock_put(sk);
 
         return mask;
 }
diff --git a/net/smc/smc.h b/net/smc/smc.h
index 51ae1f10d81a..d7ca26570482 100644
--- a/net/smc/smc.h
+++ b/net/smc/smc.h
@@ -187,11 +187,19 @@ struct smc_connection {
         struct work_struct      close_work;     /* peer sent some closing */
 };
 
+struct smc_connect_info {
+        int                     flags;
+        int                     alen;
+        struct sockaddr         addr;
+};
+
 struct smc_sock {                               /* smc sock container */
         struct sock             sk;
         struct socket           *clcsock;       /* internal tcp socket */
         struct smc_connection   conn;           /* smc connection */
         struct smc_sock         *listen_smc;    /* listen parent */
+        struct smc_connect_info *connect_info;  /* connect address & flags */
+        struct work_struct      connect_work;   /* handle non-blocking connect*/
         struct work_struct      tcp_listen_work;/* handle tcp socket accepts */
         struct work_struct      smc_listen_work;/* prepare new accept socket */
         struct list_head        accept_q;       /* sockets to be accepted */