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runtime: nil dereference on FreeBSD in runSafePointFn #19061

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ianlancetaylor opened this issue Feb 13, 2017 · 3 comments

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commented Feb 13, 2017

Seen on the builder: https://build.golang.org/log/ec4f681c914df48df85ebbfd344586f6a9ece205 .

This could be related to the commit being tested, https://golang.org/cl/36799, git revision 3792db5, though at the moment I don't see how.

##### ../test/bench/go1
fatal error: unexpected signal during runtime execution
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x42df68]

runtime stack:
runtime.throw(0x893040, 0x2a)
    /tmp/workdir/go/src/runtime/panic.go:596 +0x95
runtime.sigpanic()
    /tmp/workdir/go/src/runtime/signal_unix.go:332 +0x2db
runtime.runSafePointFn()
    /tmp/workdir/go/src/runtime/proc.go:1305 +0x58
runtime.schedule()
    /tmp/workdir/go/src/runtime/proc.go:2190 +0x2c7
runtime.park_m(0xc4200a7380)
    /tmp/workdir/go/src/runtime/proc.go:2285 +0xab
runtime.mcall(0x801400268)
    /tmp/workdir/go/src/runtime/asm_amd64.s:269 +0x5b

goroutine 1 [semacquire]:
sync.runtime_Semacquire(0xc4203e92ac)
    /tmp/workdir/go/src/runtime/sema.go:61 +0x34
sync.(*WaitGroup).Wait(0xc4203e92a0)
    /tmp/workdir/go/src/sync/waitgroup.go:131 +0x72
cmd/go/internal/work.(*Builder).Do(0xc4203ed080, 0xc4203169c0)
    /tmp/workdir/go/src/cmd/go/internal/work/build.go:1206 +0x490
cmd/go/internal/test.runTest(0xa870a0, 0xc420010120, 0x2, 0x2)
    /tmp/workdir/go/src/cmd/go/internal/test/test.go:650 +0x137c
main.main()
    /tmp/workdir/go/src/cmd/go/main.go:133 +0x841

goroutine 17 [syscall, locked to thread]:
runtime.goexit()
    /tmp/workdir/go/src/runtime/asm_amd64.s:2184 +0x1

goroutine 5 [syscall]:
os/signal.signal_recv(0x0)
    /tmp/workdir/go/src/runtime/sigqueue.go:116 +0xa7
os/signal.loop()
    /tmp/workdir/go/src/os/signal/signal_unix.go:22 +0x22
created by os/signal.init.1
    /tmp/workdir/go/src/os/signal/signal_unix.go:28 +0x41

goroutine 12 [select]:
cmd/go/internal/work.(*Builder).Do.func2(0xc4203e92a0, 0xc4203ed080, 0xc42019f740)
    /tmp/workdir/go/src/cmd/go/internal/work/build.go:1187 +0x1bd
created by cmd/go/internal/work.(*Builder).Do
    /tmp/workdir/go/src/cmd/go/internal/work/build.go:1184 +0x46f

goroutine 13 [select]:
cmd/go/internal/work.(*Builder).Do.func2(0xc4203e92a0, 0xc4203ed080, 0xc42019f740)
    /tmp/workdir/go/src/cmd/go/internal/work/build.go:1187 +0x1bd
created by cmd/go/internal/work.(*Builder).Do
    /tmp/workdir/go/src/cmd/go/internal/work/build.go:1184 +0x46f

goroutine 14 [runnable]:
syscall.Syscall(0x6, 0x6, 0x0, 0x0, 0x0, 0x0, 0x0)
    /tmp/workdir/go/src/syscall/asm_unix_amd64.s:19 +0x5
syscall.Close(0x6, 0xc4204e2fe0, 0x8)
    /tmp/workdir/go/src/syscall/zsyscall_freebsd_amd64.go:377 +0x4a
syscall.forkExec(0xc4202608a0, 0x2b, 0xc42025e4d0, 0xb, 0xb, 0xc4204e3168, 0x20, 0x410e7d, 0xc420156700)
    /tmp/workdir/go/src/syscall/exec_unix.go:203 +0x469
syscall.StartProcess(0xc4202608a0, 0x2b, 0xc42025e4d0, 0xb, 0xb, 0xc4204e3168, 0x2, 0x4, 0x20, 0x20)
    /tmp/workdir/go/src/syscall/exec_unix.go:240 +0x64
os.startProcess(0xc4202608a0, 0x2b, 0xc42025e4d0, 0xb, 0xb, 0xc4204e3310, 0x20, 0xc4201566e0, 0x0)
    /tmp/workdir/go/src/os/exec_posix.go:45 +0x1fb
os.StartProcess(0xc4202608a0, 0x2b, 0xc42025e4d0, 0xb, 0xb, 0xc4204e3310, 0x0, 0x0, 0xc4200a6680)
    /tmp/workdir/go/src/os/exec.go:94 +0x64
os/exec.(*Cmd).Start(0xc4204b6580, 0x0, 0xc42033ca80)
    /tmp/workdir/go/src/os/exec/exec.go:359 +0x502
os/exec.(*Cmd).Run(0xc4204b6580, 0xc42033ca80, 0x0)
    /tmp/workdir/go/src/os/exec/exec.go:277 +0x2b
cmd/go/internal/work.(*Builder).runOut(0xc4203ed080, 0x881a45, 0x1, 0x883f7d, 0x8, 0x0, 0x0, 0x0, 0xc4204e3688, 0x7, ...)
    /tmp/workdir/go/src/cmd/go/internal/work/build.go:1956 +0x429
cmd/go/internal/work.(*Builder).run(0xc4203ed080, 0x881a45, 0x1, 0x883f7d, 0x8, 0x0, 0x0, 0x0, 0xc4204e3688, 0x7, ...)
    /tmp/workdir/go/src/cmd/go/internal/work/build.go:1901 +0xc2
cmd/go/internal/work.gcToolchain.ld(0xc4203ed080, 0xc420316410, 0xc4202c7b80, 0x45, 0xc42049a000, 0x73, 0x80, 0xc4202c7a90, 0x43, 0x0, ...)
    /tmp/workdir/go/src/cmd/go/internal/work/build.go:2435 +0x88e
cmd/go/internal/work.(*gcToolchain).ld(0xaaa370, 0xc4203ed080, 0xc420316410, 0xc4202c7b80, 0x45, 0xc42049a000, 0x73, 0x80, 0xc4202c7a90, 0x43, ...)
    <autogenerated>:1 +0xeb
cmd/go/internal/work.(*Builder).build(0xc4203ed080, 0xc420316410, 0x0, 0x0)
    /tmp/workdir/go/src/cmd/go/internal/work/build.go:1461 +0x20d1
cmd/go/internal/work.(*Builder).Do.func1(0xc420316410)
    /tmp/workdir/go/src/cmd/go/internal/work/build.go:1138 +0x72
cmd/go/internal/work.(*Builder).Do.func2(0xc4203e92a0, 0xc4203ed080, 0xc42019f740)
    /tmp/workdir/go/src/cmd/go/internal/work/build.go:1197 +0x145
created by cmd/go/internal/work.(*Builder).Do
    /tmp/workdir/go/src/cmd/go/internal/work/build.go:1184 +0x46f

goroutine 15 [select]:
cmd/go/internal/work.(*Builder).Do.func2(0xc4203e92a0, 0xc4203ed080, 0xc42019f740)
    /tmp/workdir/go/src/cmd/go/internal/work/build.go:1187 +0x1bd
created by cmd/go/internal/work.(*Builder).Do
    /tmp/workdir/go/src/cmd/go/internal/work/build.go:1184 +0x46f

@ianlancetaylor ianlancetaylor added this to the Go1.9 milestone Feb 13, 2017

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commented Feb 13, 2017

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commented Feb 13, 2017

FYI the FreeBSD builder has now passed twice since that CL, so this is most likely not related to the CL.

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commented May 18, 2017

This has appeared twice on the dashboard:

$ greplogs -dashboard -E "runtime.runSafePointFn" -l -md
2017-02-13T18:36:28-3792db5/freebsd-amd64-gce93
2017-03-02T23:30:07-9b15c13/freebsd-amd64-gce101

The crash is clearly because sched.safePointFn is nil. I've checked over the synchronization around this carefully and I don't see anything wrong (and while there's some complex stuff going on, the non-nil-ness of runSafePointFn is pretty simple). I also checked over the generated assembly to make sure the compiler wasn't messing up the ordering of the atomics.

However, in all three cases, we're also in the middle of a forkExec. And all three failures are on FreeBSD. Hence, I strongly suspect that this is actually a dup of the infamous #15658.

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