runtime: use pidfd to wait for processes on Linux

Use pidfd_open and poll on newer versions of Linux to wait
for the process to exit. For older versions use existing wait logic

Fixes: #5617

Signed-off-by: Alexandru Matei <alexandru.matei@uipath.com>

src/runtime/virtcontainers/utils/utils_linux.go

@@ -14,8 +14,10 @@ import (
 	"os"
 	"strings"
 	"syscall"
+	"time"
 	"unsafe"
 
+	"github.com/sirupsen/logrus"
 	"golang.org/x/sys/unix"
 )
 
@@ -151,3 +153,60 @@ func IsAPVFIOMediatedDevice(sysfsdev string) bool {
 	}
 	return false
 }
+
+func waitProcessUsingPidfd(pid int, timeoutSecs uint, logger *logrus.Entry) (bool, error) {
+	pidfd, err := unix.PidfdOpen(pid, 0)
+
+	if err != nil {
+		if err == unix.ESRCH {
+			return false, nil
+		}
+
+		return true, err
+	}
+
+	defer unix.Close(pidfd)
+	var n int
+
+	maxDelay := time.Duration(timeoutSecs) * time.Second
+	end := time.Now().Add(maxDelay)
+
+	for {
+		remaining := time.Until(end).Milliseconds()
+		if remaining < 0 {
+			remaining = 0
+		}
+
+		n, err = unix.Poll([]unix.PollFd{{Fd: int32(pidfd), Events: unix.POLLIN}}, int(remaining))
+		if err != unix.EINTR {
+			break
+		}
+	}
+
+	if err != nil || n != 1 {
+		logger.Warnf("process %v still running after waiting %ds", pid, timeoutSecs)
+		return true, err
+	}
+
+	for {
+		err := unix.Waitid(unix.P_PIDFD, pidfd, nil, unix.WEXITED, nil)
+		if err == unix.EINVAL {
+			err = unix.Waitid(unix.P_PID, pid, nil, unix.WEXITED, nil)
+		}
+
+		if err != unix.EINTR {
+			break
+		}
+	}
+	return false, nil
+}
+
+func waitForProcessCompletion(pid int, timeoutSecs uint, logger *logrus.Entry) bool {
+	pidRunning, err := waitProcessUsingPidfd(pid, timeoutSecs, logger)
+
+	if err == unix.ENOSYS {
+		pidRunning = waitProcessUsingWaitLoop(pid, timeoutSecs, logger)
+	}
+
+	return pidRunning
+}