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cmd/compile: deadlock while typechecking self-referential constraint #49439

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aarzilli opened this issue Nov 8, 2021 · 6 comments
Closed

cmd/compile: deadlock while typechecking self-referential constraint #49439

aarzilli opened this issue Nov 8, 2021 · 6 comments
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FrozenDueToAge NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. release-blocker
Milestone
Go1.18

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@aarzilli
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aarzilli commented Nov 8, 2021

Compiling this (wrong) code:

package main

type X[T any, PT X[T]] interface{}

causes a deadlock (I think it's trying to infer the second parameter):

fatal error: all goroutines are asleep - deadlock!

goroutine 1 [semacquire]:
sync.runtime_SemacquireMutex(0x0?, 0xe8?, 0x29?)
	/usr/local/go/src/runtime/sema.go:71 +0x25
sync.(*Mutex).lockSlow(0xc0004140f4)
	/usr/local/go/src/sync/mutex.go:153 +0x165
sync.(*Mutex).Lock(...)
	/usr/local/go/src/sync/mutex.go:81
sync.(*Once).doSlow(0x200?, 0xc00037cb98?)
	/usr/local/go/src/sync/once.go:64 +0x53
sync.(*Once).Do(...)
	/usr/local/go/src/sync/once.go:59
cmd/compile/internal/types2.(*Named).resolve(0xc000414080?, 0x9e?)
	/usr/local/go/src/cmd/compile/internal/types2/named.go:44 +0x5d
cmd/compile/internal/types2.asNamed(...)
	/usr/local/go/src/cmd/compile/internal/types2/type.go:74
cmd/compile/internal/types2.under({0xe85550?, 0xc000414080?})
	/usr/local/go/src/cmd/compile/internal/types2/type.go:24 +0x56
cmd/compile/internal/types2.(*TypeParam).iface(0xc000400450)
	/usr/local/go/src/cmd/compile/internal/types2/typeparam.go:84 +0x37
cmd/compile/internal/types2.(*TypeParam).underIs(0xe85640?, 0xc000400450?)
	/usr/local/go/src/cmd/compile/internal/types2/typeparam.go:138 +0x1e
cmd/compile/internal/types2.underIs({0xe85640?, 0xc000400450?}, 0xc00037ccd0)
	/usr/local/go/src/cmd/compile/internal/types2/expr.go:165 +0x52
...
@ALTree ALTree added this to the Go1.18 milestone Nov 8, 2021
@ALTree ALTree added NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. release-blocker labels Nov 8, 2021
@cuonglm
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cuonglm commented Nov 8, 2021

This trybot failure seems a variant of this issue: https://storage.googleapis.com/go-build-log/09876462/linux-amd64-unified_f935df09.log

@findleyr findleyr self-assigned this Nov 8, 2021
@findleyr
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findleyr commented Nov 8, 2021

This doesn't appear to be fixed by the revert of CL 362254.

I'm investigating.

@findleyr
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findleyr commented Nov 8, 2021

This is a consequence of https://golang.org/cl/356489, which allowed inferring type instances and introduced a vector for recursive expansion.

I'll fix this instance, and will add a more general mechanism for detecting recursive expansion.

@gopherbot
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Change https://golang.org/cl/361922 mentions this issue: cmd/compile/internal/types2: disallow type cycles through type parameter lists

@griesemer
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CL 361922 is a bit of a hammer, but it seems that uniform type inference is more important than type parameter lists that recurse with types to which those type parameter lists belong.

@gopherbot
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Change https://go.dev/cl/386718 mentions this issue: go/types: refine the check for invalid cycles through tparam lists

@nekomeowww nekomeowww mentioned this issue Jun 15, 2023
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cmd/compile: ignore cycles for recursive generic fields golangFame/go
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@aarzilli @ALTree @cuonglm @griesemer @gopherbot @findleyr