runtime: only increment extraMInUse when actually in use
Currently lockextra always increments extraMInUse, even if the M won't
be used (or doesn't even exist), such as in addExtraM. addExtraM fails
to decrement extraMInUse, so it stays elevated forever.
Fix this bug and simplify the model by moving extraMInUse out of
lockextra to getExtraM, where we know the M will actually be used.
While we're here, remove the nilokay argument from getExtraM, which is
always false.
Fixes #60540.
Change-Id: I7a5d97456b3bc6ea1baeb06b5b2975e3b8dd96a0
Reviewed-on: https://go-review.googlesource.com/c/go/+/499677 Reviewed-by: Cherry Mui <cherryyz@google.com>
Auto-Submit: Michael Pratt <mpratt@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>