Commit 6f57e56a authored by Claudio Imbrenda's avatar Claudio Imbrenda Committed by David S. Miller
Browse files

Revert "vsock: Fix blocking ops call in prepare_to_wait" 

This reverts commit 59888180 ("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: default avatarClaudio Imbrenda <imbrenda@linux.vnet.ibm.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 9a0384c0

net/vmw_vsock/af_vsock.c

+13 −6
Original line number Diff line number Diff line
@@ -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;

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