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>

1 files changed, 13 insertions, 6 deletions

diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index bbe65dcb9738..7fd1220fbfa0 100644
--- 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;