runtime: hold sched.lock over traceThreadDestroy in dropm

This is required by traceThreadDestroy, though it's not strictly
necessary in this case. The requirement to hold sched.lock comes from
the assumption that traceThreadDestroy is getting called when the thread
leaves the tracer's view, but in this case the extra m that dropm is
dropping never leaves the allm list. Nevertheless, traceThreadDestroy
requires it just as a safety measure, and that's reasonable. dropm is
generally rare on pthread platforms, so the extra lock acquire over this
short critical section (and only when tracing is enabled) is fine.

Change-Id: Ib631820963c74f2f087d14a0067d0441d75d6785
Reviewed-on: https://go-review.googlesource.com/c/go/+/544396
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

0 files changed, 0 insertions, 0 deletions