Use Task blocking timer for nanosleep(2).

kernel/time.Timer allocation is expensive and not sync.Poolable (since
time.Timer only supports notification through a channel, requiring a goroutine
to receive from the channel, and sync.Pool doesn't invoke any kind of cleanup
on discarded items in the pool so it would leak timer goroutines). Using the
existing Task.blockingTimer for nanosleep(), and applicable cases in
clock_nanosleep(), at least avoids Timer allocation in common cases.

PiperOrigin-RevId: 406248394

Author: nixprime

pkg/sentry/syscalls/linux/sys_time.go

@@ -175,73 +175,6 @@ func Time(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallC
 	return uintptr(r), nil, nil
 }
 
-// clockNanosleepRestartBlock encapsulates the state required to restart
-// clock_nanosleep(2) via restart_syscall(2).
-//
-// +stateify savable
-type clockNanosleepRestartBlock struct {
-	c   ktime.Clock
-	end ktime.Time
-	rem hostarch.Addr
-}
-
-// Restart implements kernel.SyscallRestartBlock.Restart.
-func (n *clockNanosleepRestartBlock) Restart(t *kernel.Task) (uintptr, error) {
-	return 0, clockNanosleepUntil(t, n.c, n.end, n.rem, true)
-}
-
-// clockNanosleepUntil blocks until a specified time.
-//
-// If blocking is interrupted, the syscall is restarted with the original
-// arguments.
-func clockNanosleepUntil(t *kernel.Task, c ktime.Clock, end ktime.Time, rem hostarch.Addr, needRestartBlock bool) error {
-	notifier, tchan := ktime.NewChannelNotifier()
-	timer := ktime.NewTimer(c, notifier)
-
-	// Turn on the timer.
-	timer.Swap(ktime.Setting{
-		Period:  0,
-		Enabled: true,
-		Next:    end,
-	})
-
-	err := t.BlockWithTimer(nil, tchan)
-
-	timer.Destroy()
-
-	switch {
-	case linuxerr.Equals(linuxerr.ETIMEDOUT, err):
-		// Slept for entire timeout.
-		return nil
-	case err == linuxerr.ErrInterrupted:
-		// Interrupted.
-		remaining := end.Sub(c.Now())
-		if remaining <= 0 {
-			return nil
-		}
-
-		// Copy out remaining time.
-		if rem != 0 {
-			timeleft := linux.NsecToTimespec(remaining.Nanoseconds())
-			if err := copyTimespecOut(t, rem, &timeleft); err != nil {
-				return err
-			}
-		}
-		if needRestartBlock {
-			// Arrange for a restart with the remaining duration.
-			t.SetSyscallRestartBlock(&clockNanosleepRestartBlock{
-				c:   c,
-				end: end,
-				rem: rem,
-			})
-			return linuxerr.ERESTART_RESTARTBLOCK
-		}
-		return linuxerr.ERESTARTNOHAND
-	default:
-		panic(fmt.Sprintf("Impossible BlockWithTimer error %v", err))
-	}
-}
-
 // Nanosleep implements linux syscall Nanosleep(2).
 func Nanosleep(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
 	addr := args[0].Pointer()
@@ -279,10 +212,12 @@ func ClockNanosleep(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kerne
 		return 0, nil, linuxerr.EINVAL
 	}
 
-	// Only allow clock constants also allowed by Linux.
+	// Only allow clock constants also allowed by Linux. (CLOCK_TAI is
+	// unimplemented.)
 	if clockID > 0 {
 		if clockID != linux.CLOCK_REALTIME &&
 			clockID != linux.CLOCK_MONOTONIC &&
+			clockID != linux.CLOCK_BOOTTIME &&
 			clockID != linux.CLOCK_PROCESS_CPUTIME_ID {
 			return 0, nil, linuxerr.EINVAL
 		}
@@ -301,6 +236,74 @@ func ClockNanosleep(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kerne
 	return 0, nil, clockNanosleepUntil(t, c, c.Now().Add(dur), rem, true)
 }
 
+// clockNanosleepUntil blocks until a specified time.
+//
+// If blocking is interrupted, the syscall is restarted with the original
+// arguments.
+func clockNanosleepUntil(t *kernel.Task, c ktime.Clock, end ktime.Time, rem hostarch.Addr, needRestartBlock bool) error {
+	var err error
+	if c == t.Kernel().MonotonicClock() {
+		err = t.BlockWithDeadline(nil, true, end)
+	} else {
+		notifier, tchan := ktime.NewChannelNotifier()
+		timer := ktime.NewTimer(c, notifier)
+		timer.Swap(ktime.Setting{
+			Period:  0,
+			Enabled: true,
+			Next:    end,
+		})
+		err = t.BlockWithTimer(nil, tchan)
+		timer.Destroy()
+	}
+
+	switch {
+	case linuxerr.Equals(linuxerr.ETIMEDOUT, err):
+		// Slept for entire timeout.
+		return nil
+	case err == linuxerr.ErrInterrupted:
+		// Interrupted.
+		remaining := end.Sub(c.Now())
+		if remaining <= 0 {
+			return nil
+		}
+
+		// Copy out remaining time.
+		if rem != 0 {
+			timeleft := linux.NsecToTimespec(remaining.Nanoseconds())
+			if err := copyTimespecOut(t, rem, &timeleft); err != nil {
+				return err
+			}
+		}
+		if needRestartBlock {
+			// Arrange for a restart with the remaining duration.
+			t.SetSyscallRestartBlock(&clockNanosleepRestartBlock{
+				c:   c,
+				end: end,
+				rem: rem,
+			})
+			return linuxerr.ERESTART_RESTARTBLOCK
+		}
+		return linuxerr.ERESTARTNOHAND
+	default:
+		panic(fmt.Sprintf("Impossible BlockWithTimer error %v", err))
+	}
+}
+
+// clockNanosleepRestartBlock encapsulates the state required to restart
+// clock_nanosleep(2) via restart_syscall(2).
+//
+// +stateify savable
+type clockNanosleepRestartBlock struct {
+	c   ktime.Clock
+	end ktime.Time
+	rem hostarch.Addr
+}
+
+// Restart implements kernel.SyscallRestartBlock.Restart.
+func (n *clockNanosleepRestartBlock) Restart(t *kernel.Task) (uintptr, error) {
+	return 0, clockNanosleepUntil(t, n.c, n.end, n.rem, true)
+}
+
 // Gettimeofday implements linux syscall gettimeofday(2).
 func Gettimeofday(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
 	tv := args[0].Pointer()