runtime: track goroutine location until actual STW
TestTraceSTW / TestTraceGCSTW currently tracks the location (M/P) of the
target goroutines until it reaches the "start" log message, assuming the
actual STW comes immediately afterwards.
On 386 with TestTraceGCSTW, it actually tends to take >10ms after the
start log before the STW actually occurs. This is enough time for sysmon
to preempt the target goroutines and migration them to another location.
Fix this by continuing tracking all the way until the STW itself occurs.
We still keep the start log message so we can ignore any STW (if any)
before we expect.
Cq-Include-Trybots: luci.golang.try:gotip-linux-386-longtest,gotip-linux-amd64-longtest
Change-Id: I6a6a636cf2dcb18d8b33ac4ad88333cabff2eabb
Reviewed-on: https://go-review.googlesource.com/c/go/+/722520 Reviewed-by: Michael Knyszek <mknyszek@google.com>
Auto-Submit: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>