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runtime: checkptrAlignment crash on nil pointer #47430

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mdempsky opened this issue Jul 28, 2021 · 7 comments
Closed

runtime: checkptrAlignment crash on nil pointer #47430

mdempsky opened this issue Jul 28, 2021 · 7 comments
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FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done. release-blocker
Milestone
Go1.17

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@mdempsky
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With Go 1.17rc1 (and probably since 4bb0847), this program crashes when run with checkptr enabled (e.g., with -race):

package main

import (
	"runtime"
	"time"
	"unsafe"
)

func main() {
	go func() {
		for {
			runtime.GC()
		}
	}()

	go func() {
		for i := 0; ; i++ {
			recurse(i % 1024)
		}
	}()

	time.Sleep(time.Second)
}

func recurse(n int) {
	// Inflate the stack so runtime.shrinkstack gets called during GC
	if n > 0 {
		recurse(n - 1)
	}

	var p unsafe.Pointer
	_ = (*int)(p)
}

Easy fix is adding an explicit nil check at the start of checkptrAlignment.
@mdempsky mdempsky added the NeedsFix The path to resolution is known, but the work has not been done. label Jul 28, 2021
@mdempsky mdempsky added this to the Go1.17 milestone Jul 28, 2021
@mdempsky mdempsky self-assigned this Jul 28, 2021
@gopherbot
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Change https://golang.org/cl/338029 mentions this issue: runtime: don't crash on nil pointers in checkptrAlignment

@mdempsky
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@golang/release Do I need to do anything to make sure b39e0f4 is included in Go 1.17?

It's a runtime bug that causes valid programs to sporadically fail, albeit only when checkptr is enabled (e.g., when the race detector or msan are used).

@mdempsky mdempsky reopened this Jul 28, 2021
@cagedmantis
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@mdempsky It's marked as a release blocker which means Go 1.17 will not be released until the issue is resolved. This will probably block a second release candidate as well.

@cagedmantis
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I realize that I didn't answer the question explicitly. The @golang/release will ensure it is included in the Go 1.17 release.

@toothrot
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@mdempsky Is there more work to do on this issue, or is it resolved by the linked CL?

@mdempsky
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@cagedmantis Thanks!

@toothrot The issue is fixed by b39e0f4. I just reopened for discussion purposes to make sure it wasn't missed. I think we can close it if there's no procedural reason to keep it open any more.

@toothrot
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@mdempsky We've got it, thanks!

@golang golang locked and limited conversation to collaborators Jun 23, 2023
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FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done. release-blocker
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@toothrot @mdempsky @cagedmantis @gopherbot