monitor: Fix monitor race condition doing hypervisor.check()

The thread monitor will check if the agent and the VMM are alive every
second in a blocking thread. The Cloud hypervisor API server is
single-threaded, if the monitor does a `check()`, while a slow request
is still in progress, the monitor check() method will timeout. The
monitor thread will stop all the shim-v2 execution.

This commit modifies the monitor thread to make it check the status of
the hypervisor after 5 seconds. Additionally, the `check()` method from
cloud-hypervisor will use the method `clh.isClhRunning(timeout)` with a
10 seconds timeout. The monitor function does no timeout, so even if
`hypervisor.check()` takes more 10 seconds, the isClhRunning method
handles errors doing a VmmPing and retry in case of errors until the
timeout is reached.

Reduce the time to the next check to 5 should not affect any functionality,
but it will reduce the overhead polling the hypervisor.

Fixes: #2777

Signed-off-by: Carlos Venegas <jose.carlos.venegas.munoz@intel.com>

src/runtime/virtcontainers/clh.go

@@ -761,12 +761,18 @@ func (clh *cloudHypervisor) Load(s persistapi.HypervisorState) {
 	clh.state.apiSocket = s.APISocket
 }
 
-func (clh *cloudHypervisor) Check() error {
+// Check is the implementation of Check from the Hypervisor interface.
-	cl := clh.client()
+// Check if the VMM API is working.
-	ctx, cancel := context.WithTimeout(context.Background(), clhAPITimeout*time.Second)
-	defer cancel()
 
-	_, _, err := cl.VmmPingGet(ctx)
+func (clh *cloudHypervisor) Check() error {
+	// Use a long timeout to check if the VMM is running:
+	// Check is used by the monitor thread(a background thread). If the
+	// monitor thread calls Check() during the Container boot, it will take
+	// longer than usual specially if there is a hot-plug request in progress.
+	running, err := clh.isClhRunning(10)
+	if !running {
+		return fmt.Errorf("clh is not running: %s", err)
+	}
 	return err
 }
 
@@ -1034,8 +1040,6 @@ func (clh *cloudHypervisor) isClhRunning(timeout uint) (bool, error) {
 
 	pid := clh.state.PID
 
-	// Check if clh process is running, in case it is not, let's
-	// return from here.
 	if err := syscall.Kill(pid, syscall.Signal(0)); err != nil {
 		return false, nil
 	}
@@ -1048,6 +1052,8 @@ func (clh *cloudHypervisor) isClhRunning(timeout uint) (bool, error) {
 		_, _, err := cl.VmmPingGet(ctx)
 		if err == nil {
 			return true, nil
+		} else {
+			clh.Logger().WithError(err).Warning("clh.VmmPingGet API call failed")
 		}
 
 		if time.Since(timeStart).Seconds() > float64(timeout) {

src/runtime/virtcontainers/monitor.go

@@ -14,7 +14,7 @@ import (
 )
 
 const (
-	defaultCheckInterval = 1 * time.Second
+	defaultCheckInterval = 5 * time.Second
 	watcherChannelSize   = 128
 )