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vm-virtio: Ensure pause event is caught by every virtio thread

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Each virtio thread was reading/draining the pause_evt pipe when
detecting the associated event. Problem is, when a virtio device has
multiple threads, they all share the same pause_evt pipe, which can
prevent some threads from receiving the event. If the first thread to
catch the event is quickly clearing the pipe, some other threads might
simply miss the event and they will not enter the "paused" state as
expected.

This is a behavior that was spotted with virtio-net as it usually uses
2 threads by default (1 for TX/RX queues and 1 for the control queue).

The way to solve this issue is by letting each thread drain the pipe
during the resume codepath, that is after the thread has been unparked.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
This commit is contained in:
Sebastien Boeuf
2020-06-25 10:08:05 +02:00
parent 86377127df
commit a7f0f9dfea
10 changed files with 50 additions and 18 deletions
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7
vm-virtio/src/vhost_user/handler.rs
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@@ -163,8 +163,6 @@ impl<S: VhostUserMasterReqHandler> VhostUserEpollHandler<S> {
break 'poll;
}
x if pause_evt_index == x => {
// Drain pause event
let _ = self.vu_epoll_cfg.pause_evt.read();
debug!("PAUSE_EVENT received, pausing vhost-user epoll loop");
// We loop here to handle spurious park() returns.
// Until we have not resumed, the paused boolean will
@@ -172,6 +170,11 @@ impl<S: VhostUserMasterReqHandler> VhostUserEpollHandler<S> {
while paused.load(Ordering::SeqCst) {
thread::park();
}
// Drain pause event after the device has been resumed.
// This ensures the pause event has been seen by each
// and every thread related to this virtio device.
let _ = self.vu_epoll_cfg.pause_evt.read();
}
x if (slave_evt_index.is_some() && slave_evt_index.unwrap() == x) => {
if let Some(slave_req_handler) =