fix process termination handling for runc exec

This patch makes the process handling consistent between runc.Run and
runc.Exec usage.  Previously runc.Run would use context.Background
for the runc.Run process and would monitor the request context for
shutdown requests, sending a SIGKILL to the container pid1 process. This
allowed runc.Run to gracefully shutdown and reap child processes.  This
logic was not used for runc.Exec where instead we were passing in the
request context to runc.Exec, and if that request context was cancelled
the runc process would immediately terminate preventing runc from reaping
the child process.  In this scenario the extra pid will remain forever
and then when the pid1 process will get wedged in zap_pid_ns_processes
syscall upon shutdown waiting fo the zombie pid to exit.

With this fix both runc.Run and runc.Exec will use context.Background
for runc processes and monitor the request context for shutdown request
triggering a SIGKILL to the pid being monitored by runc.

Signed-off-by: coryb <[email protected]>

Author: coryb

executor/runcexecutor/executor.go

@@ -92,7 +92,7 @@ func New(opt Opt, networkProviders map[pb.NetMode]network.Provider) (executor.Ex
 
 	root := opt.Root
 
-	if err := os.MkdirAll(root, 0711); err != nil {
+	if err := os.MkdirAll(root, 0o711); err != nil {
 		return nil, errors.Wrapf(err, "failed to create %s", root)
 	}
 
@@ -205,7 +205,7 @@ func (w *runcExecutor) Run(ctx context.Context, id string, root executor.Mount,
 	}
 	bundle := filepath.Join(w.root, id)
 
-	if err := os.Mkdir(bundle, 0711); err != nil {
+	if err := os.Mkdir(bundle, 0o711); err != nil {
 		return err
 	}
 	defer os.RemoveAll(bundle)
@@ -216,7 +216,7 @@ func (w *runcExecutor) Run(ctx context.Context, id string, root executor.Mount,
 	}
 
 	rootFSPath := filepath.Join(bundle, "rootfs")
-	if err := idtools.MkdirAllAndChown(rootFSPath, 0700, identity); err != nil {
+	if err := idtools.MkdirAllAndChown(rootFSPath, 0o700, identity); err != nil {
 		return err
 	}
 	if err := mount.All(rootMount, rootFSPath); err != nil {
@@ -270,7 +270,7 @@ func (w *runcExecutor) Run(ctx context.Context, id string, root executor.Mount,
 		return errors.Wrapf(err, "working dir %s points to invalid target", newp)
 	}
 	if _, err := os.Stat(newp); err != nil {
-		if err := idtools.MkdirAllAndChown(newp, 0755, identity); err != nil {
+		if err := idtools.MkdirAllAndChown(newp, 0o755, identity); err != nil {
 			return errors.Wrapf(err, "failed to create working directory %s", newp)
 		}
 	}
@@ -287,50 +287,17 @@ func (w *runcExecutor) Run(ctx context.Context, id string, root executor.Mount,
 		return err
 	}
 
-	// runCtx/killCtx is used for extra check in case the kill command blocks
-	runCtx, cancelRun := context.WithCancel(context.Background())
-	defer cancelRun()
-
-	ended := make(chan struct{})
-	go func() {
-		for {
-			select {
-			case <-ctx.Done():
-				killCtx, timeout := context.WithTimeout(context.Background(), 7*time.Second)
-				if err := w.runc.Kill(killCtx, id, int(syscall.SIGKILL), nil); err != nil {
-					bklog.G(ctx).Errorf("failed to kill runc %s: %+v", id, err)
-					select {
-					case <-killCtx.Done():
-						timeout()
-						cancelRun()
-						return
-					default:
-					}
-				}
-				timeout()
-				select {
-				case <-time.After(50 * time.Millisecond):
-				case <-ended:
-					return
-				}
-			case <-ended:
-				return
-			}
-		}
-	}()
-
 	bklog.G(ctx).Debugf("> creating %s %v", id, meta.Args)
 
 	trace.SpanFromContext(ctx).AddEvent("Container created")
-	err = w.run(runCtx, id, bundle, process, func() {
+	err = w.run(ctx, id, bundle, process, func() {
 		startedOnce.Do(func() {
 			trace.SpanFromContext(ctx).AddEvent("Container started")
 			if started != nil {
 				close(started)
 			}
 		})
 	})
-	close(ended)
 	return exitError(ctx, err)
 }
 
@@ -462,23 +429,87 @@ func (s *forwardIO) Stderr() io.ReadCloser {
 	return nil
 }
 
-// startingProcess is to track the os process so we can send signals to it.
-type startingProcess struct {
-	Process *os.Process
-	ready   chan struct{}
+// procHandle is to track the os process so we can send signals to it.
+type procHandle struct {
+	Process  *os.Process
+	ready    chan struct{}
+	ended    chan struct{}
+	shutdown func()
 }
 
-// Release will free resources with a startingProcess.
-func (p *startingProcess) Release() {
+// runcProcessHandle will create a procHandle that will be monitored, where
+// on ctx.Done the process will be killed.  If the kill fails, then the cancel
+// will be called.  This is to allow for runc to go through its normal shutdown
+// procedure if the ctx is canceled and to ensure there are no zombie processes
+// left by runc.
+func runcProcessHandle(ctx context.Context, id string) (*procHandle, context.Context) {
+	runcCtx, cancel := context.WithCancel(context.Background())
+	p := &procHandle{
+		ready:    make(chan struct{}),
+		ended:    make(chan struct{}),
+		shutdown: cancel,
+	}
+	// preserve the logger on the context used for the runc process handling
+	runcCtx = bklog.WithLogger(runcCtx, bklog.G(ctx))
+
+	go func() {
+		// Wait for pid
+		select {
+		case <-ctx.Done():
+			return // nothing to kill
+		case <-p.ready:
+		}
+
+		for {
+			select {
+			case <-ctx.Done():
+				killCtx, timeout := context.WithTimeout(context.Background(), 7*time.Second)
+				if err := p.Process.Kill(); err != nil {
+					bklog.G(ctx).Errorf("failed to kill runc %s: %+v", id, err)
+					select {
+					case <-killCtx.Done():
+						timeout()
+						cancel()
+						return
+					default:
+					}
+				}
+				timeout()
+				select {
+				case <-time.After(50 * time.Millisecond):
+				case <-p.ended:
+					return
+				}
+			case <-p.ended:
+				return
+			}
+		}
+	}()
+
+	return p, runcCtx
+}
+
+// Release will free resources with a procHandle.
+func (p *procHandle) Release() {
+	close(p.ended)
 	if p.Process != nil {
 		p.Process.Release()
 	}
 }
 
+// Shutdown should be called after the runc process has exited. This will allow
+// the signal handling and tty resize loops to exit, terminating the
+// goroutines.
+func (p *procHandle) Shutdown() {
+	if p.shutdown != nil {
+		p.shutdown()
+	}
+}
+
 // WaitForReady will wait until the Process has been populated or the
 // provided context was cancelled.  This should be called before using
 // the Process field.
-func (p *startingProcess) WaitForReady(ctx context.Context) error {
+func (p *procHandle) WaitForReady(ctx context.Context) error {
 	select {
 	case <-ctx.Done():
 		return ctx.Err()
@@ -490,7 +521,7 @@ func (p *startingProcess) WaitForReady(ctx context.Context) error {
 // WaitForStart will record the pid reported by Runc via the channel.
 // We wait for up to 10s for the runc process to start.  If the started
 // callback is non-nil it will be called after receiving the pid.
-func (p *startingProcess) WaitForStart(ctx context.Context, startedCh <-chan int, started func()) error {
+func (p *procHandle) WaitForStart(ctx context.Context, startedCh <-chan int, started func()) error {
 	startedCtx, timeout := context.WithTimeout(ctx, 10*time.Second)
 	defer timeout()
 	var err error
@@ -515,7 +546,7 @@ func (p *startingProcess) WaitForStart(ctx context.Context, startedCh <-chan int
 
 // handleSignals will wait until the runcProcess is ready then will
 // send each signal received on the channel to the process.
-func handleSignals(ctx context.Context, runcProcess *startingProcess, signals <-chan syscall.Signal) error {
+func handleSignals(ctx context.Context, runcProcess *procHandle, signals <-chan syscall.Signal) error {
 	if signals == nil {
 		return nil
 	}

executor/runcexecutor/executor_common.go

@@ -49,23 +49,20 @@ type runcCall func(ctx context.Context, started chan<- int, io runc.IO) error
 // is only supported for linux, so this really just handles signal propagation
 // to the started runc process.
 func (w *runcExecutor) commonCall(ctx context.Context, id, bundle string, process executor.ProcessInfo, started func(), call runcCall) error {
-	runcProcess := &startingProcess{
-		ready: make(chan struct{}),
-	}
+	runcProcess, ctx := runcProcessHandle(ctx, id)
 	defer runcProcess.Release()
 
-	var eg errgroup.Group
-	egCtx, cancel := context.WithCancel(ctx)
+	eg, ctx := errgroup.WithContext(ctx)
 	defer eg.Wait()
-	defer cancel()
+	defer runcProcess.Shutdown()
 
 	startedCh := make(chan int, 1)
 	eg.Go(func() error {
-		return runcProcess.WaitForStart(egCtx, startedCh, started)
+		return runcProcess.WaitForStart(ctx, startedCh, started)
 	})
 
 	eg.Go(func() error {
-		return handleSignals(egCtx, runcProcess, process.Signal)
+		return handleSignals(ctx, runcProcess, process.Signal)
 	})
 
 	return call(ctx, startedCh, &forwardIO{stdin: process.Stdin, stdout: process.Stdout, stderr: process.Stderr})

executor/runcexecutor/executor_linux.go

@@ -44,23 +44,20 @@ func (w *runcExecutor) exec(ctx context.Context, id, bundle string, specsProcess
 type runcCall func(ctx context.Context, started chan<- int, io runc.IO) error
 
 func (w *runcExecutor) callWithIO(ctx context.Context, id, bundle string, process executor.ProcessInfo, started func(), call runcCall) error {
-	runcProcess := &startingProcess{
-		ready: make(chan struct{}),
-	}
+	runcProcess, ctx := runcProcessHandle(ctx, id)
 	defer runcProcess.Release()
 
-	var eg errgroup.Group
-	egCtx, cancel := context.WithCancel(ctx)
+	eg, ctx := errgroup.WithContext(ctx)
 	defer eg.Wait()
-	defer cancel()
+	defer runcProcess.Shutdown()
 
 	startedCh := make(chan int, 1)
 	eg.Go(func() error {
-		return runcProcess.WaitForStart(egCtx, startedCh, started)
+		return runcProcess.WaitForStart(ctx, startedCh, started)
 	})
 
 	eg.Go(func() error {
-		return handleSignals(egCtx, runcProcess, process.Signal)
+		return handleSignals(ctx, runcProcess, process.Signal)
 	})
 
 	if !process.Meta.Tty {
@@ -84,7 +81,7 @@ func (w *runcExecutor) callWithIO(ctx context.Context, id, bundle string, proces
 		}
 		pts.Close()
 		ptm.Close()
-		cancel() // this will shutdown resize and signal loops
+		runcProcess.Shutdown()
 		err := eg.Wait()
 		if err != nil {
 			bklog.G(ctx).Warningf("error while shutting down tty io: %s", err)
@@ -119,13 +116,13 @@ func (w *runcExecutor) callWithIO(ctx context.Context, id, bundle string, proces
 	}
 
 	eg.Go(func() error {
-		err := runcProcess.WaitForReady(egCtx)
+		err := runcProcess.WaitForReady(ctx)
 		if err != nil {
 			return err
 		}
 		for {
 			select {
-			case <-egCtx.Done():
+			case <-ctx.Done():
 				return nil
 			case resize := <-process.Resize:
 				err = ptm.Resize(console.WinSize{