Simplify synchronization between runsc and sandbox process

Make 'runsc create' join cgroup before creating sandbox process.
This removes the need to synchronize platform creation and ensure
that sandbox process is charged to the right cgroup from the start.

PiperOrigin-RevId: 227166451
Change-Id: Ieb4b18e6ca0daf7b331dc897699ca419bc5ee3a2

1 files changed, 7 insertions, 16 deletions

diff --git a/runsc/cmd/boot.go b/runsc/cmd/boot.go
index 192df7d3c..bb3435284 100644
--- a/runsc/cmd/boot.go
+++ b/runsc/cmd/boot.go
@@ -159,14 +159,6 @@ func (b *Boot) Execute(_ context.Context, f *flag.FlagSet, args ...interface{})
 		panic("setCapsAndCallSelf must never return success")
 	}
 
-	// Wait until this process has been moved into cgroups.
-	startSyncFile := os.NewFile(uintptr(b.startSyncFD), "start-sync file")
-	defer startSyncFile.Close()
-	buf := make([]byte, 1)
-	if r, err := startSyncFile.Read(buf); err != nil || r != 1 {
-		Fatalf("Unable to read from the start-sync descriptor: %v", err)
-	}
-
 	// Create the loader.
 	bootArgs := boot.Args{
 		ID:           f.Arg(0),
@@ -186,21 +178,20 @@ func (b *Boot) Execute(_ context.Context, f *flag.FlagSet, args ...interface{})
 		Fatalf("error creating loader: %v", err)
 	}
 
-	// Fatalf exits the process and doesn't run defers. 'l' must be destroyed
-	// explicitly!
+	// Fatalf exits the process and doesn't run defers.
+	// 'l' must be destroyed explicitly after this point!
 
-	// Notify the parent process the controller has been created.
+	// Notify the parent process the sandbox has booted (and that the controller
+	// is up).
+	startSyncFile := os.NewFile(uintptr(b.startSyncFD), "start-sync file")
+	buf := make([]byte, 1)
 	if w, err := startSyncFile.Write(buf); err != nil || w != 1 {
 		l.Destroy()
 		Fatalf("Unable to write into the start-sync descriptor: %v", err)
 	}
-	// startSyncFile is closed here to be sure that starting with this point
-	// the runsc process will not write anything into it.
+	// Closes startSyncFile because 'l.Run()' only returns when the sandbox exits.
 	startSyncFile.Close()
 
-	// Notify other processes the loader has been created.
-	l.NotifyLoaderCreated()
-
 	// Wait for the start signal from runsc.
 	l.WaitForStartSignal()