From 6b26788c55d2c1e874e6321b8ce33f1a2c0270e6 Mon Sep 17 00:00:00 2001
From: Austin Clements <[email protected]>
Date: Mon, 23 Nov 2015 15:03:38 -0500
Subject: [PATCH 62/63] [release-branch.go1.5] runtime: take stack barrier lock
 during copystack

Commit bbd1a1c prevented SIGPROF from scanning stacks that were being
copied, but it didn't prevent a stack copy (specifically a stack
shrink) from happening while SIGPROF is scanning the stack. As a
result, a stack copy may adjust stack barriers while SIGPROF is in the
middle of scanning a stack, causing SIGPROF to panic when it detects
an inconsistent stack barrier.

Fix this by taking the stack barrier lock while adjusting the stack.
In addition to preventing SIGPROF from scanning this stack, this will
block until any in-progress SIGPROF is done scanning the stack.

For 1.5.2.

Fixes #13362.
Updates #12932.

Change-Id: I422219c363054410dfa56381f7b917e04690e5dd
Reviewed-on: https://go-review.googlesource.com/17191
Run-TryBot: Austin Clements <[email protected]>
Reviewed-by: Russ Cox <[email protected]>
Run-TryBot: Russ Cox <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-on: https://go-review.googlesource.com/17194
---
 src/runtime/stack1.go | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/runtime/stack1.go b/src/runtime/stack1.go
index efcb5f2..19634ef 100644
--- a/src/runtime/stack1.go
+++ b/src/runtime/stack1.go
@@ -609,6 +609,10 @@ func copystack(gp *g, newsize uintptr) {
 		print("copystack gp=", gp, " [", hex(old.lo), " ", hex(old.hi-used), " ", hex(old.hi), "]/", gp.stackAlloc, " -> [", hex(new.lo), " ", hex(new.hi-used), " ", hex(new.hi), "]/", newsize, "\n")
 	}
 
+	// Disallow sigprof scans of this stack and block if there's
+	// one in progress.
+	gcLockStackBarriers(gp)
+
 	// adjust pointers in the to-be-copied frames
 	var adjinfo adjustinfo
 	adjinfo.old = old
@@ -640,6 +644,8 @@ func copystack(gp *g, newsize uintptr) {
 	gp.stackAlloc = newsize
 	gp.stkbar = newstkbar
 
+	gcUnlockStackBarriers(gp)
+
 	// free old stack
 	if stackPoisonCopy != 0 {
 		fillstack(old, 0xfc)
-- 
2.6.1