Maybe an infinite loop occurs during gc?

[crazycomputer]

What version of Go are you using (go version)?

$ go version go1.12.4 linux/arm64

Does this issue reproduce with the latest release?

sorry, I didn't try to reproduce it with the latest release

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GOARCH="arm64"
GOBIN=""
GOCACHE="/root/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="arm64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/usr/local/gopkg"
GOPROXY=""
GORACE=""
GOROOT="/usr/local/go"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_arm64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build266632096=/tmp/go-build -gno-record-gcc-switches"

What did you do?

I compiled an executable file and executed it.But looks like that it didn't enter the main function.And I checked the CPU usage of this process with command "pidstat -P", I found that one thread of the process occupied 100% of the CPU in user space. So I tried to debug it with gdb.

The call stack I saw is as follows:

#0  runtime.pidleget () at /usr/local/go/src/runtime/proc.go:4711
#1  runtime.stopTheWorldWithSema () at /usr/local/go/src/runtime/proc.go:1036
#2  0x0000000000459ff8 in runtime.systemstack () at /usr/local/go/src/runtime/asm_arm64.s:237
#3  0x0000000000433938 in runtime.startTheWorldWithSema (emitTraceEvent=224, ~r1=<optimized out>) at /usr/local/go/src/runtime/proc.go:1082
Backtrace stopped: previous frame identical to this frame (corrupt stack?)
![image](https://user-images.githubusercontent.com/34932896/68009045-bf4ba380-fcbb-11e9-9de6-cc5addc6aa75.png)

I made a breakpoint at runtime.pidleget (),and saw that it always enter this method.It looks like a infiniteloop.It always can get idle p when call runtime.pidleget ().Then I printed the runtime.sched to see why an infinite loop occurs.

(gdb) p 'runtime.sched'
$22 = {goidgen = 81, lastpoll = 0, lock = {key = 2}, midle = 274881896448, nmidle = 2, nmidlelocked = 1, mnext = 14, maxmcount = 10000, nmsys = 2, nmfreed = 0, ngsys = 17, **pidle = 274878131968**, npidle = 2895823215, nmspinning = 0, runq = {head = 0, tail = 0}, 
  runqsize = 0, disable = {user = false, runnable = {head = 0, tail = 0}, n = 0}, gFree = {lock = {key = 0}, stack = {head = 0}, noStack = {head = 0}, n = 0}, sudoglock = {key = 0}, sudogcache = 0x0, deferlock = {key = 0}, deferpool = {0x0, 0x0, 0x0, 0x0, 0x0}, 
  freem = 0x0, gcwaiting = 1, stopwait = -1399144080, stopnote = {key = 0}, sysmonwait = 0, sysmonnote = {key = 0}, safePointFn = {void (runtime.p *)} 0x1335600 <runtime.sched>, safePointWait = 0, safePointNote = {key = 0}, profilehz = 0, 
  procresizetime = 97197470357832, totaltime = 0}
(gdb) c
Continuing.

Thread 1 "*****" hit Breakpoint 1, runtime.pidleget () at /usr/local/go/src/runtime/proc.go:4711
4711		if _p_ != nil {
(gdb) p 'runtime.sched'
$23 = {goidgen = 81, lastpoll = 0, lock = {key = 2}, midle = 274881896448, nmidle = 2, nmidlelocked = 1, mnext = 14, maxmcount = 10000, nmsys = 2, nmfreed = 0, ngsys = 17, **pidle = 274878103552,** npidle = 2895823214, nmspinning = 0, runq = {head = 0, tail = 0}, 
  runqsize = 0, disable = {user = false, runnable = {head = 0, tail = 0}, n = 0}, gFree = {lock = {key = 0}, stack = {head = 0}, noStack = {head = 0}, n = 0}, sudoglock = {key = 0}, sudogcache = 0x0, deferlock = {key = 0}, deferpool = {0x0, 0x0, 0x0, 0x0, 0x0}, 
  freem = 0x0, gcwaiting = 1, stopwait = -1399144081, stopnote = {key = 0}, sysmonwait = 0, sysmonnote = {key = 0}, safePointFn = {void (runtime.p *)} 0x1335600 <runtime.sched>, safePointWait = 0, safePointNote = {key = 0}, profilehz = 0, 
  procresizetime = 97197470357832, totaltime = 0}
(gdb) c
Continuing.

Thread 1 "*****" hit Breakpoint 1, runtime.pidleget () at /usr/local/go/src/runtime/proc.go:4711
4711		if _p_ != nil {
(gdb) p 'runtime.sched'
$24 = {goidgen = 81, lastpoll = 0, lock = {key = 2}, midle = 274881896448, nmidle = 2, nmidlelocked = 1, mnext = 14, maxmcount = 10000, nmsys = 2, nmfreed = 0, ngsys = 17, **pidle = 274878113024**, npidle = 2895823213, nmspinning = 0, runq = {head = 0, tail = 0}, 
  runqsize = 0, disable = {user = false, runnable = {head = 0, tail = 0}, n = 0}, gFree = {lock = {key = 0}, stack = {head = 0}, noStack = {head = 0}, n = 0}, sudoglock = {key = 0}, sudogcache = 0x0, deferlock = {key = 0}, deferpool = {0x0, 0x0, 0x0, 0x0, 0x0}, 
  freem = 0x0, gcwaiting = 1, stopwait = -1399144082, stopnote = {key = 0}, sysmonwait = 0, sysmonnote = {key = 0}, safePointFn = {void (runtime.p *)} 0x1335600 <runtime.sched>, safePointWait = 0, safePointNote = {key = 0}, profilehz = 0, 
  procresizetime = 97197470357832, totaltime = 0}
(gdb) c
Continuing.

Thread 1 "*****" hit Breakpoint 1, runtime.pidleget () at /usr/local/go/src/runtime/proc.go:4711
4711		if _p_ != nil {
(gdb) p 'runtime.sched'
$25 = {goidgen = 81, lastpoll = 0, lock = {key = 2}, midle = 274881896448, nmidle = 2, nmidlelocked = 1, mnext = 14, maxmcount = 10000, nmsys = 2, nmfreed = 0, ngsys = 17, **pidle = 274878141440**, npidle = 2895823212, nmspinning = 0, runq = {head = 0, tail = 0}, 
  runqsize = 0, disable = {user = false, runnable = {head = 0, tail = 0}, n = 0}, gFree = {lock = {key = 0}, stack = {head = 0}, noStack = {head = 0}, n = 0}, sudoglock = {key = 0}, sudogcache = 0x0, deferlock = {key = 0}, deferpool = {0x0, 0x0, 0x0, 0x0, 0x0}, 
  freem = 0x0, gcwaiting = 1, stopwait = -1399144083, stopnote = {key = 0}, sysmonwait = 0, sysmonnote = {key = 0}, safePointFn = {void (runtime.p *)} 0x1335600 <runtime.sched>, safePointWait = 0, safePointNote = {key = 0}, profilehz = 0, 
  procresizetime = 97197470357832, totaltime = 0}
(gdb) c
Continuing.

Thread 1 "*****" hit Breakpoint 1, runtime.pidleget () at /usr/local/go/src/runtime/proc.go:4711
4711		if _p_ != nil {
(gdb) p 'runtime.sched'
$26 = {goidgen = 81, lastpoll = 0, lock = {key = 2}, midle = 274881896448, nmidle = 2, nmidlelocked = 1, mnext = 14, maxmcount = 10000, nmsys = 2, nmfreed = 0, ngsys = 17, **pidle = 274878131968**, npidle = 2895823211, nmspinning = 0, runq = {head = 0, tail = 0}, 
  runqsize = 0, disable = {user = false, runnable = {head = 0, tail = 0}, n = 0}, gFree = {lock = {key = 0}, stack = {head = 0}, noStack = {head = 0}, n = 0}, sudoglock = {key = 0}, sudogcache = 0x0, deferlock = {key = 0}, deferpool = {0x0, 0x0, 0x0, 0x0, 0x0}, 
  freem = 0x0, gcwaiting = 1, stopwait = -1399144084, stopnote = {key = 0}, sysmonwait = 0, sysmonnote = {key = 0}, safePointFn = {void (runtime.p *)} 0x1335600 <runtime.sched>, safePointWait = 0, safePointNote = {key = 0}, profilehz = 0, 
  procresizetime = 97197470357832, totaltime = 0}

The pidle pointer looks like a circular linked list，the npidle has been reduced to a reversal.
I don't think this should ever happen.In this case .It will circulate infinitely and never end.

Can anyone help me?
3ks

What did you expect to see?

What did you see instead?

[ianlancetaylor]

Looks like you have memory corruption. Does this problem happen consistently? Does your program use unsafe or call C code?

[crazycomputer]

@ianlancetaylor
Thanks for your reply. Program don't use usafe or C code.And I didn't access runtime.sched directly. This problem happens Accidentally.
I can't make sure it would happen in which case.
But when I compiled and ran the same code on arch amd64,this problem never happen.

[ianlancetaylor]

Is there a way that we can reproduce the problem ourselves?

[ianlancetaylor]

Also, is it possible for you try Go 1.13.4?

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