From 9f9b95bb59176d4b9e381265ea49a8fe15a5f3c1 Mon Sep 17 00:00:00 2001

From: Austin Clements <[email protected]>

Date: Mon, 23 Nov 2015 11:29:56 -0500

Subject: [PATCH 61/63] [release-branch.go1.5] runtime: improve stack barrier

 debugging

This improves stack barrier debugging messages in various ways:

1) Rather than printing only the remaining stack barriers (of which

   there may be none, which isn't very useful), print all of the G's

   stack barriers with a marker at the position the stack itself has

   unwound to and a marker at the problematic stack barrier (where

   applicable).

2) Rather than crashing if we encounter a stack barrier when there are

   no more stkbar entries, print the same debug message we would if we

   had encountered a stack barrier at an unexpected location.

Hopefully this will help with debugging #12528.

Change-Id: I2e6fe6a778e0d36dd8ef30afd4c33d5d94731262

Reviewed-on: https://go-review.googlesource.com/17147

Reviewed-by: Rick Hudson <[email protected]>

Reviewed-by: Russ Cox <[email protected]>

Reviewed-on: https://go-review.googlesource.com/17193

Run-TryBot: Austin Clements <[email protected]>

TryBot-Result: Gobot Gobot <[email protected]>

---

 src/runtime/mgcmark.go   | 28 ++++++++++++++++++++++------

 src/runtime/traceback.go | 16 +++++++++-------

 2 files changed, 31 insertions(+), 13 deletions(-)

diff --git a/src/runtime/mgcmark.go b/src/runtime/mgcmark.go

index ac93e16..151a8bd 100644

--- a/src/runtime/mgcmark.go

+++ b/src/runtime/mgcmark.go

@@ -608,22 +608,36 @@ func gcRemoveStackBarrier(gp *g, stkbar stkbar) {

 		printlock()

 		print("at *", hex(stkbar.savedLRPtr), " expected stack barrier PC ", hex(stackBarrierPC), ", found ", hex(val), ", goid=", gp.goid, "\n")

 		print("gp.stkbar=")

-		gcPrintStkbars(gp.stkbar)

-		print(", gp.stkbarPos=", gp.stkbarPos, ", gp.stack=[", hex(gp.stack.lo), ",", hex(gp.stack.hi), ")\n")

+		gcPrintStkbars(gp, -1)

+		print(", gp.stack=[", hex(gp.stack.lo), ",", hex(gp.stack.hi), ")\n")

 		throw("stack barrier lost")

 	}

 	*lrPtr = uintreg(stkbar.savedLRVal)

 }

-// gcPrintStkbars prints a []stkbar for debugging.

-func gcPrintStkbars(stkbar []stkbar) {

+// gcPrintStkbars prints the stack barriers of gp for debugging. It

+// places a "@@@" marker at gp.stkbarPos. If marker >= 0, it will also

+// place a "==>" marker before the marker'th entry.

+func gcPrintStkbars(gp *g, marker int) {

 	print("[")

-	for i, s := range stkbar {

+	for i, s := range gp.stkbar {

 		if i > 0 {

 			print(" ")

 		}

+		if i == int(gp.stkbarPos) {

+			print("@@@ ")

+		}

+		if i == marker {

+			print("==> ")

+		}

 		print("*", hex(s.savedLRPtr), "=", hex(s.savedLRVal))

 	}

+	if int(gp.stkbarPos) == len(gp.stkbar) {

+		print(" @@@")

+	}

+	if marker == len(gp.stkbar) {

+		print(" ==>")

+	}

 	print("]")

 }

@@ -648,7 +662,9 @@ func gcUnwindBarriers(gp *g, sp uintptr) {

 	gcUnlockStackBarriers(gp)

 	if debugStackBarrier && gp.stkbarPos != before {

 		print("skip barriers below ", hex(sp), " in goid=", gp.goid, ": ")

-		gcPrintStkbars(gp.stkbar[before:gp.stkbarPos])

+		// We skipped barriers between the "==>" marker

+		// (before) and the "@@@" marker (gp.stkbarPos).

+		gcPrintStkbars(gp, int(before))

 		print("\n")

 	}

 }

diff --git a/src/runtime/traceback.go b/src/runtime/traceback.go

index 8f27ba4..fa13713 100644

--- a/src/runtime/traceback.go

+++ b/src/runtime/traceback.go

@@ -142,7 +142,8 @@ func gentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max in

 	// Fix up returns to the stack barrier by fetching the

 	// original return PC from gp.stkbar.

-	stkbar := gp.stkbar[gp.stkbarPos:]

+	stkbarG := gp

+	stkbar := stkbarG.stkbar[stkbarG.stkbarPos:]

 	if pc0 == ^uintptr(0) && sp0 == ^uintptr(0) { // Signal to fetch saved values from gp.

 		if gp.syscallsp != 0 {

@@ -206,8 +207,8 @@ func gentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max in

 			stkbarPos = gp.stkbarPos - 1

 		} else {

 			printlock()

-			print("runtime: failed to unwind through stackBarrier at SP ", hex(sp0), " index ", gp.stkbarPos, "; ")

-			gcPrintStkbars(gp.stkbar)

+			print("runtime: failed to unwind through stackBarrier at SP ", hex(sp0), "; ")

+			gcPrintStkbars(gp, int(gp.stkbarPos))

 			print("\n")

 			throw("inconsistent state in stackBarrier")

 		}

@@ -244,7 +245,8 @@ func gentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max in

 			sp := frame.sp

 			if flags&_TraceJumpStack != 0 && f.entry == systemstackPC && gp == g.m.g0 && gp.m.curg != nil {

 				sp = gp.m.curg.sched.sp

-				stkbar = gp.m.curg.stkbar[gp.m.curg.stkbarPos:]

+				stkbarG = gp.m.curg

+				stkbar = stkbarG.stkbar[stkbarG.stkbarPos:]

 			}

 			frame.fp = sp + uintptr(funcspdelta(f, frame.pc))

 			if !usesLR {

@@ -282,9 +284,9 @@ func gentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max in

 			}

 			if frame.lr == stackBarrierPC {

 				// Recover original PC.

-				if stkbar[0].savedLRPtr != lrPtr {

+				if len(stkbar) == 0 || stkbar[0].savedLRPtr != lrPtr {

 					print("found next stack barrier at ", hex(lrPtr), "; expected ")

-					gcPrintStkbars(stkbar)

+					gcPrintStkbars(stkbarG, len(stkbarG.stkbar)-len(stkbar))

 					print("\n")

 					throw("missed stack barrier")

 				}

@@ -504,7 +506,7 @@ func gentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max in

 	if callback != nil && n < max && len(stkbar) > 0 {

 		print("runtime: g", gp.goid, ": leftover stack barriers ")

-		gcPrintStkbars(stkbar)

+		gcPrintStkbars(stkbarG, len(stkbarG.stkbar)-len(stkbar))

 		print("\n")

 		throw("traceback has leftover stack barriers")

 	}

-- 

2.6.1