runsc: add global profile collection flags

Add global flags -profile-{block,cpu,heap,mutex} and -trace which
enable collection of the specified profile for the entire duration of a
container execution. This provides a way to definitively start profiling
before that application starts, rather than attempting to race with an
out-of-band `runsc debug`.

Note that only the main boot process is profiled.

This exposed a bug in Task.traceExecEvent: a crash when tracing and
-race are enabled. traceExecEvent is called off of the task goroutine,
but uses the Task as a context, which is a violation of the Task
contract. Switching to the AsyncContext fixes the issue.

Fixes #220

1 files changed, 5 insertions, 1 deletions

diff --git a/pkg/sentry/kernel/task_log.go b/pkg/sentry/kernel/task_log.go
index 8de08151a..c5b099559 100644
--- a/pkg/sentry/kernel/task_log.go
+++ b/pkg/sentry/kernel/task_log.go
@@ -249,5 +249,9 @@ func (t *Task) traceExecEvent(image *TaskImage) {
 		return
 	}
 	defer file.DecRef(t)
-	trace.Logf(t.traceContext, traceCategory, "exec: %s", file.PathnameWithDeleted(t))
+
+	// traceExecEvent function may be called before the task goroutine
+	// starts, so we must use the async context.
+	name := file.PathnameWithDeleted(t.AsyncContext())
+	trace.Logf(t.traceContext, traceCategory, "exec: %s", name)
 }