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Revert "vsock: Fix blocking ops call in prepare_to_wait"

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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>
This commit is contained in:
Claudio Imbrenda 2016-03-22 17:05:51 +01:00 committed by David S. Miller
parent 9a0384c020
commit 6f57e56a15
1 changed files with 13 additions and 6 deletions
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19
net/vmw_vsock/af_vsock.c
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@ -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;