1 files changed, 28 insertions, 7 deletions
diff --git a/pkg/sentry/kernel/semaphore/semaphore.go b/pkg/sentry/kernel/semaphore/semaphore.go
index 310762936..b99c0bffa 100644
--- a/pkg/sentry/kernel/semaphore/semaphore.go
+++ b/pkg/sentry/kernel/semaphore/semaphore.go
@@ -103,6 +103,7 @@ type waiter struct {
 	waiterEntry
 
 	// value represents how much resource the waiter needs to wake up.
+	// The value is either 0 or negative.
 	value int16
 	ch    chan struct{}
 }
@@ -423,8 +424,7 @@ func (s *Set) GetPID(num int32, creds *auth.Credentials) (int32, error) {
 	return sem.pid, nil
 }
 
-// GetZeroWaiters returns number of waiters waiting for the sem to go to zero.
-func (s *Set) GetZeroWaiters(num int32, creds *auth.Credentials) (uint16, error) {
+func (s *Set) countWaiters(num int32, creds *auth.Credentials, pred func(w *waiter) bool) (uint16, error) {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 
@@ -437,13 +437,27 @@ func (s *Set) GetZeroWaiters(num int32, creds *auth.Credentials) (uint16, error)
 	if sem == nil {
 		return 0, syserror.ERANGE
 	}
-	var semzcnt uint16
+	var cnt uint16
 	for w := sem.waiters.Front(); w != nil; w = w.Next() {
-		if w.value == 0 {
-			semzcnt++
+		if pred(w) {
+			cnt++
 		}
 	}
-	return semzcnt, nil
+	return cnt, nil
+}
+
+// CountZeroWaiters returns number of waiters waiting for the sem's value to increase.
+func (s *Set) CountZeroWaiters(num int32, creds *auth.Credentials) (uint16, error) {
+	return s.countWaiters(num, creds, func(w *waiter) bool {
+		return w.value == 0
+	})
+}
+
+// CountNegativeWaiters returns number of waiters waiting for the sem to go to zero.
+func (s *Set) CountNegativeWaiters(num int32, creds *auth.Credentials) (uint16, error) {
+	return s.countWaiters(num, creds, func(w *waiter) bool {
+		return w.value < 0
+	})
 }
 
 // ExecuteOps attempts to execute a list of operations to the set. It only
@@ -598,11 +612,18 @@ func (s *Set) destroy() {
 	}
 }
 
+func abs(val int16) int16 {
+	if val < 0 {
+		return -val
+	}
+	return val
+}
+
 // wakeWaiters goes over all waiters and checks which of them can be notified.
 func (s *sem) wakeWaiters() {
 	// Note that this will release all waiters waiting for 0 too.
 	for w := s.waiters.Front(); w != nil; {
-		if s.value < w.value {
+		if s.value < abs(w.value) {
 			// Still blocked, skip it.
 			w = w.Next()
 			continue