When an M's use of a lock causes delays in other Ms, capture the stack
of the unlock call that caused the delay. This makes the meaning of the
mutex profile for runtime-internal mutexes match the behavior for
sync.Mutex: the profile points to the end of the critical section that
is responsible for delaying other work.
Fixes #66999
Change-Id: I4abc4a1df00a48765d29c07776481a1cbd539ff8
Reviewed-on: https://go-review.googlesource.com/c/go/+/585638
Auto-Submit: Rhys Hiltner <rhys.hiltner@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Carlos Amedee <carlos@golang.org> Reviewed-by: Michael Pratt <mpratt@google.com>