Revert "vsock: Fix blocking ops call in prepare_to_wait"

This reverts commit 5988818008257ca42010d6b43a3e0e48afec9898 ("vsock: Fix
blocking ops call in prepare_to_wait")

The commit reverted with this patch caused us to potentially miss wakeups.
Since the condition is not checked between the prepare_to_wait and the
schedule(), if a wakeup happens after the condition is checked but before
the sleep happens, we will miss it. ( A description of the problem can be
found here: http://www.makelinux.net/ldd3/chp-6-sect-2 ).

By reverting the patch, the behaviour is still incorrect (since we
shouldn't sleep between the prepare_to_wait and the schedule) but at least
it will not miss wakeups.

The next patch in the series actually fixes the behaviour.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index bbe65dcb973834761c30cef249a537ba498898fb..7fd1220fbfa0bb2477e2b7e6edcf714a5ae6a097 100644 (file)
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -1557,6 +1557,8 @@ static int vsock_stream_sendmsg(struct socket *sock, struct msghdr *msg,
        if (err < 0)
                goto out;
 
+       prepare_to_wait(sk_sleep(sk), &wait, TASK_INTERRUPTIBLE);
+
        while (total_written < len) {
                ssize_t written;
 
@@ -1576,9 +1578,7 @@ static int vsock_stream_sendmsg(struct socket *sock, struct msghdr *msg,
                                goto out_wait;
 
                        release_sock(sk);
-                       prepare_to_wait(sk_sleep(sk), &wait, TASK_INTERRUPTIBLE);
                        timeout = schedule_timeout(timeout);
-                       finish_wait(sk_sleep(sk), &wait);
                        lock_sock(sk);
                        if (signal_pending(current)) {
                                err = sock_intr_errno(timeout);
@@ -1588,6 +1588,8 @@ static int vsock_stream_sendmsg(struct socket *sock, struct msghdr *msg,
                                goto out_wait;
                        }
 
+                       prepare_to_wait(sk_sleep(sk), &wait,
+                                       TASK_INTERRUPTIBLE);
                }
 
                /* These checks occur both as part of and after the loop
@@ -1633,6 +1635,7 @@ static int vsock_stream_sendmsg(struct socket *sock, struct msghdr *msg,
 out_wait:
        if (total_written > 0)
                err = total_written;
+       finish_wait(sk_sleep(sk), &wait);
 out:
        release_sock(sk);
        return err;
@@ -1713,6 +1716,7 @@ vsock_stream_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
        if (err < 0)
                goto out;
 
+       prepare_to_wait(sk_sleep(sk), &wait, TASK_INTERRUPTIBLE);
 
        while (1) {
                s64 ready = vsock_stream_has_data(vsk);
@@ -1723,7 +1727,7 @@ vsock_stream_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
                         */
 
                        err = -ENOMEM;
-                       goto out;
+                       goto out_wait;
                } else if (ready > 0) {
                        ssize_t read;
 
@@ -1746,7 +1750,7 @@ vsock_stream_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
                                        vsk, target, read,
                                        !(flags & MSG_PEEK), &recv_data);
                        if (err < 0)
-                               goto out;
+                               goto out_wait;
 
                        if (read >= target || flags & MSG_PEEK)
                                break;
@@ -1769,9 +1773,7 @@ vsock_stream_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
                                break;
 
                        release_sock(sk);
-                       prepare_to_wait(sk_sleep(sk), &wait, TASK_INTERRUPTIBLE);
                        timeout = schedule_timeout(timeout);
-                       finish_wait(sk_sleep(sk), &wait);
                        lock_sock(sk);
 
                        if (signal_pending(current)) {
@@ -1781,6 +1783,9 @@ vsock_stream_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
                                err = -EAGAIN;
                                break;
                        }
+
+                       prepare_to_wait(sk_sleep(sk), &wait,
+                                       TASK_INTERRUPTIBLE);
                }
        }
 
@@ -1811,6 +1816,8 @@ vsock_stream_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
                err = copied;
        }
 
+out_wait:
+       finish_wait(sk_sleep(sk), &wait);
 out:
        release_sock(sk);
        return err;