After kernel upgrade, we faced some stalled communication on HyperV VMs
with our golang clients. We bisected the issue to patch
[b3f7fd54881bcba5dc529935f38] af_vsock: separate wait data loop
When this occurred the following sequence appeared in ftrace:
hvs_stream_has_data <- vsock_connectible_wait_data
hvs_channel_cb <- vmbus_on_event
hvs_notify_recv_pre_block <- vsock_connectible_wait_data
It turned out that it was possible to enter hvs_notify_recv_pre_block
with data pending in the stream. This is because the data condition must
be checked between prepare_to_wait and schedule, if not the receiver may
not be woken up if an event occurs after checking the condition and
before prepare_to_wait. This patch moves prepare_to_wait call before
the condition and at the end of loop, similar to what is done elsewhere
in the same file.
Signed-off-by: Frédéric Dalleau <frederic.dalleau@xxxxxxxxxx>
---
net/vmw_vsock/af_vsock.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index ee418701cdee..cd5e0dbcabe0 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -1904,9 +1904,9 @@ static int vsock_connectible_wait_data(struct sock *sk,
vsk = vsock_sk(sk);
err = 0;
transport = vsk->transport;
+ prepare_to_wait(sk_sleep(sk), wait, TASK_INTERRUPTIBLE);
while ((data = vsock_connectible_has_data(vsk)) == 0) {
- prepare_to_wait(sk_sleep(sk), wait, TASK_INTERRUPTIBLE);
if (sk->sk_err != 0 ||
(sk->sk_shutdown & RCV_SHUTDOWN) ||
@@ -1937,6 +1937,7 @@ static int vsock_connectible_wait_data(struct sock *sk,
err = -EAGAIN;
break;
}
+ prepare_to_wait(sk_sleep(sk), wait, TASK_INTERRUPTIBLE);
}
finish_wait(sk_sleep(sk), wait);
--
2.34.1
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