From: Austin Clements <austin@google.com>
Date: Mon, 17 Oct 2016 01:22:02 +0000 (-0400)
Subject: runtime: keep gcMarkRootCheck happy with spare Gs
X-Git-Tag: go1.8beta1~750
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=2be3ab441578413972d93fc1048decc422640b09;p=gostls13.git

runtime: keep gcMarkRootCheck happy with spare Gs

oneNewExtraM creates a spare M and G for use with cgo callbacks. The G
doesn't run right away, but goes directly into syscall status. For the
garbage collector, it's marked as "scan valid" and not on the rescan
list, but I forgot to also mark it as "scan done". As a result,
gcMarkRootCheck thinks that the goroutine hasn't been scanned and
panics.

This only affects GODEBUG=gccheckmark=1 mode, since we otherwise skip
the gcMarkRootCheck.

Fixes #17473.

Change-Id: I94f5671c42eb44bd5ea7dc68fbf85f0c19e2e52c
Reviewed-on: https://go-review.googlesource.com/31139
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>
---

diff --git a/src/runtime/proc.go b/src/runtime/proc.go
index 937135961a..f68a189997 100644
--- a/src/runtime/proc.go
+++ b/src/runtime/proc.go
@@ -1449,6 +1449,7 @@ func oneNewExtraM() {
 	gp.syscallsp = gp.sched.sp
 	gp.stktopsp = gp.sched.sp
 	gp.gcscanvalid = true // fresh G, so no dequeueRescan necessary
+	gp.gcscandone = true
 	gp.gcRescan = -1
 	// malg returns status as Gidle, change to Gsyscall before adding to allg
 	// where GC will see it.