From: Austin Clements <austin@google.com>
Date: Tue, 24 May 2016 02:05:51 +0000 (-0400)
Subject: runtime: document scanstack
X-Git-Tag: go1.7beta1~91
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=a1f7db88f8c70a7520ce870a71706032f173739f;p=gostls13.git

runtime: document scanstack

Also mark it go:systemstack and explain why.

Change-Id: I88baf22741c04012ba2588d8e03dd3801d19b5c0
Reviewed-on: https://go-review.googlesource.com/23390
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/mgcmark.go b/src/runtime/mgcmark.go
index cbdf2b8375..b0e7477d50 100644
--- a/src/runtime/mgcmark.go
+++ b/src/runtime/mgcmark.go
@@ -642,7 +642,17 @@ func gcFlushBgCredit(scanWork int64) {
 	unlock(&work.assistQueue.lock)
 }
 
+// scanstack scans gp's stack, greying all pointers found on the stack.
+//
+// During mark phase, it also installs stack barriers while traversing
+// gp's stack. During mark termination, it stops scanning when it
+// reaches an unhit stack barrier.
+//
+// scanstack is marked go:systemstack because it must not be preempted
+// while using a workbuf.
+//
 //go:nowritebarrier
+//go:systemstack
 func scanstack(gp *g) {
 	if gp.gcscanvalid {
 		return