cmd/trace: don't filter events for profile by whether they have stack
Right now the profile-from-trace code blindly discards events that don't
have a stack, but this means it can discard 'end' events for goroutine
time ranges that don't have stacks, like when a goroutine exits a
syscall. This means we drop stack samples we *do* have, because we
correctly already only use the stack trace of the corresponding 'start'
event for a time-range-of-interest anyway.
This change means that some events will be tracked that have no stack in
their start event, but that's fine. It won't end up in the profile
anyway because the stack is empty! And the rest of the code appears to
be robust to an empty stack already.
Thank you to Rhys Hiltner for reporting this issue and for the
reproducer, which I have worked into a test for this change.
Fixes #74850.
Change-Id: I943b97ecf6b82803e4a778a0f83a14473d32254e
Reviewed-on: https://go-review.googlesource.com/c/go/+/694156 Reviewed-by: Rhys Hiltner <rhys.hiltner@gmail.com> Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Carlos Amedee <carlos@golang.org>