Revert "runtime: push down systemstack requirement for tracer where possible"

This reverts CL 572095.

Reason for revert: Broke longtest builders.

Change-Id: Iac3a8159d3afb4156a49c7d6819cdd15fe9d4bbb
Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-longtest
Reviewed-on: https://go-review.googlesource.com/c/go/+/577376
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>

1 files changed, 8 insertions, 5 deletions

diff --git a/src/runtime/trace2stack.go b/src/runtime/trace2stack.go
index 7d698c89d3..4ee3b32b05 100644
--- a/src/runtime/trace2stack.go
+++ b/src/runtime/trace2stack.go
@@ -138,6 +138,11 @@ func (t *traceStackTable) put(pcs []uintptr) uint64 {
 // dump writes all previously cached stacks to trace buffers,
 // releases all memory and resets state. It must only be called once the caller
 // can guarantee that there are no more writers to the table.
+//
+// This must run on the system stack because it flushes buffers and thus
+// may acquire trace.lock.
+//
+//go:systemstack
 func (t *traceStackTable) dump(gen uintptr) {
 	w := unsafeTraceWriter(gen, nil)
 
@@ -189,11 +194,9 @@ func (t *traceStackTable) dump(gen uintptr) {
 	}
 	// Still, hold the lock over reset. The callee expects it, even though it's
 	// not strictly necessary.
-	systemstack(func() {
-		lock(&t.tab.lock)
-		t.tab.reset()
-		unlock(&t.tab.lock)
-	})
+	lock(&t.tab.lock)
+	t.tab.reset()
+	unlock(&t.tab.lock)
 
 	w.flush().end()
 }