From 9b0ea6aa271c811abc180eb46a4d114890870ec5 Mon Sep 17 00:00:00 2001
From: Austin Clements <austin@google.com>
Date: Tue, 24 Mar 2015 11:51:24 -0400
Subject: [PATCH] runtime: remove write barrier on G in sighandler

sighandler may run during a stop-the-world without a P, so it's not
allowed to have write barriers. Fix the G write to disable the write
barrier (this is safe because the G is reachable from allgs) and mark
the function nowritebarrier.

Change-Id: I907f05d3829e24eeb15fa4d020598af36710e87e
Reviewed-on: https://go-review.googlesource.com/8020
Reviewed-by: Rick Hudson <rlh@golang.org>
---
 src/runtime/os3_plan9.go     | 4 +++-
 src/runtime/signal_386.go    | 4 +++-
 src/runtime/signal_amd64x.go | 4 +++-
 src/runtime/signal_arm.go    | 4 +++-
 src/runtime/signal_arm64.go  | 4 +++-
 src/runtime/signal_ppc64x.go | 4 +++-
 6 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/src/runtime/os3_plan9.go b/src/runtime/os3_plan9.go
index 27519debd35..fa49ad681f3 100644
--- a/src/runtime/os3_plan9.go
+++ b/src/runtime/os3_plan9.go
@@ -6,6 +6,8 @@ package runtime
 
 import "unsafe"
 
+// May run during STW, so write barriers are not allowed.
+//go:nowritebarrier
 func sighandler(_ureg *ureg, note *byte, gp *g) int {
 	_g_ := getg()
 	var t sigTabT
@@ -79,7 +81,7 @@ func sighandler(_ureg *ureg, note *byte, gp *g) int {
 	}
 Throw:
 	_g_.m.throwing = 1
-	_g_.m.caughtsig = gp
+	setGNoWriteBarrier(&_g_.m.caughtsig, gp)
 	startpanic()
 	print(notestr, "\n")
 	print("PC=", hex(c.pc()), "\n")
diff --git a/src/runtime/signal_386.go b/src/runtime/signal_386.go
index 0ca593de029..b63299511f6 100644
--- a/src/runtime/signal_386.go
+++ b/src/runtime/signal_386.go
@@ -24,6 +24,8 @@ func dumpregs(c *sigctxt) {
 	print("gs     ", hex(c.gs()), "\n")
 }
 
+// May run during STW, so write barriers are not allowed.
+//go:nowritebarrier
 func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 	_g_ := getg()
 	c := &sigctxt{info, ctxt}
@@ -98,7 +100,7 @@ func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 	}
 
 	_g_.m.throwing = 1
-	_g_.m.caughtsig = gp
+	setGNoWriteBarrier(&_g_.m.caughtsig, gp)
 	startpanic()
 
 	if sig < uint32(len(sigtable)) {
diff --git a/src/runtime/signal_amd64x.go b/src/runtime/signal_amd64x.go
index cd87d76a50a..5dc9d8070a8 100644
--- a/src/runtime/signal_amd64x.go
+++ b/src/runtime/signal_amd64x.go
@@ -37,6 +37,8 @@ func dumpregs(c *sigctxt) {
 
 var crashing int32
 
+// May run during STW, so write barriers are not allowed.
+//go:nowritebarrier
 func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 	_g_ := getg()
 	c := &sigctxt{info, ctxt}
@@ -134,7 +136,7 @@ func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 	}
 
 	_g_.m.throwing = 1
-	_g_.m.caughtsig = gp
+	setGNoWriteBarrier(&_g_.m.caughtsig, gp)
 
 	if crashing == 0 {
 		startpanic()
diff --git a/src/runtime/signal_arm.go b/src/runtime/signal_arm.go
index c07b45ef18c..7d417fa2b3c 100644
--- a/src/runtime/signal_arm.go
+++ b/src/runtime/signal_arm.go
@@ -32,6 +32,8 @@ func dumpregs(c *sigctxt) {
 	print("fault   ", hex(c.fault()), "\n")
 }
 
+// May run during STW, so write barriers are not allowed.
+//go:nowritebarrier
 func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 	_g_ := getg()
 	c := &sigctxt{info, ctxt}
@@ -93,7 +95,7 @@ func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 	}
 
 	_g_.m.throwing = 1
-	_g_.m.caughtsig = gp
+	setGNoWriteBarrier(&_g_.m.caughtsig, gp)
 	startpanic()
 
 	if sig < uint32(len(sigtable)) {
diff --git a/src/runtime/signal_arm64.go b/src/runtime/signal_arm64.go
index cc8985872ca..efb84029e28 100644
--- a/src/runtime/signal_arm64.go
+++ b/src/runtime/signal_arm64.go
@@ -45,6 +45,8 @@ func dumpregs(c *sigctxt) {
 	print("fault   ", hex(c.fault()), "\n")
 }
 
+// May run during STW, so write barriers are not allowed.
+//go:nowritebarrier
 func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 	_g_ := getg()
 	c := &sigctxt{info, ctxt}
@@ -106,7 +108,7 @@ func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 	}
 
 	_g_.m.throwing = 1
-	_g_.m.caughtsig = gp
+	setGNoWriteBarrier(&_g_.m.caughtsig, gp)
 	startpanic()
 
 	if sig < uint32(len(sigtable)) {
diff --git a/src/runtime/signal_ppc64x.go b/src/runtime/signal_ppc64x.go
index 94b4708dd59..018d7d62efa 100644
--- a/src/runtime/signal_ppc64x.go
+++ b/src/runtime/signal_ppc64x.go
@@ -50,6 +50,8 @@ func dumpregs(c *sigctxt) {
 	print("trap ", hex(c.trap()), "\n")
 }
 
+// May run during STW, so write barriers are not allowed.
+//go:nowritebarrier
 func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 	_g_ := getg()
 	c := &sigctxt{info, ctxt}
@@ -111,7 +113,7 @@ func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 	}
 
 	_g_.m.throwing = 1
-	_g_.m.caughtsig = gp
+	setGNoWriteBarrier(&_g_.m.caughtsig, gp)
 	startpanic()
 
 	if sig < uint32(len(sigtable)) {