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runtime: fix deadlock in runtime.Stack
It shouldn't semacquire() inside an acquirem(), the runtime thinks that means deadlock. It actually isn't a deadlock, but it looks like it because acquirem() does m.locks++. Candidate for inclusion in 1.4.1. runtime.Stack with all=true is pretty unuseable in GOMAXPROCS>1 environment. fixes #9321 Change-Id: Iac6b664217d24763b9878c20e49229a1ecffc805 Reviewed-on: https://go-review.googlesource.com/1600 Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
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@ -564,20 +564,16 @@ func saveg(pc, sp uintptr, gp *g, r *StackRecord) {
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// If all is true, Stack formats stack traces of all other goroutines
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// into buf after the trace for the current goroutine.
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func Stack(buf []byte, all bool) int {
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mp := acquirem()
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gp := mp.curg
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if all {
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semacquire(&worldsema, false)
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mp.gcing = 1
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releasem(mp)
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gp := getg()
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gp.m.gcing = 1
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systemstack(stoptheworld)
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if mp != acquirem() {
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gothrow("Stack: rescheduled")
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}
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}
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n := 0
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if len(buf) > 0 {
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gp := getg()
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sp := getcallersp(unsafe.Pointer(&buf))
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pc := getcallerpc(unsafe.Pointer(&buf))
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systemstack(func() {
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@ -594,11 +590,11 @@ func Stack(buf []byte, all bool) int {
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}
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if all {
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mp.gcing = 0
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gp := getg()
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gp.m.gcing = 0
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semrelease(&worldsema)
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systemstack(starttheworld)
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}
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releasem(mp)
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return n
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}
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37
test/fixedbugs/issue9321.go
Normal file
37
test/fixedbugs/issue9321.go
Normal file
@ -0,0 +1,37 @@
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// run
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// Copyright 2014 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package main
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import (
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"bytes"
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"runtime"
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"runtime/pprof"
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"sync"
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)
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func test() {
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var wg sync.WaitGroup
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wg.Add(2)
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test := func() {
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for i := 0; i < 100; i++ {
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buf := &bytes.Buffer{}
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pprof.Lookup("goroutine").WriteTo(buf, 2)
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}
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wg.Done()
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}
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go test()
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go test()
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wg.Wait()
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}
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func main() {
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runtime.GOMAXPROCS(2)
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for i := 0; i < 100; i++ {
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test()
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}
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}
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