cmd/compile: deadlock

[Lumaraf]

Go version

go version go1.24.2 windows/amd64

Output of go env in your module/workspace:

set AR=ar
set CC=gcc
set CGO_CFLAGS=-O2 -g
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-O2 -g
set CGO_ENABLED=0
set CGO_FFLAGS=-O2 -g
set CGO_LDFLAGS=-O2 -g
set CXX=g++
set GCCGO=gccgo
set GO111MODULE=on
set GOAMD64=v1
set GOARCH=amd64
set GOAUTH=netrc
set GOBIN=
set GOCACHE=C:\Users\Anwender\AppData\Local\go-build
set GOCACHEPROG=
set GODEBUG=
set GOENV=C:\Users\Anwender\AppData\Roaming\go\env
set GOEXE=.exe
set GOEXPERIMENT=
set GOFIPS140=off
set GOFLAGS=
set GOGCCFLAGS=-m64 -fno-caret-diagnostics -Qunused-arguments -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=C:\Users\Anwender\AppData\Local\Temp\go-build380231616=/tmp/go-build -gno-record-gcc-switches
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOINSECURE=
set GOMOD=E:\workspace\sudoku-solver\go.mod
set GOMODCACHE=C:\Users\Anwender\go\pkg\mod
set GONOPROXY=
set GONOSUMDB=
set GOOS=windows
set GOPATH=C:\Users\Anwender\go
set GOPRIVATE=
set GOPROXY=https://proxy.golang.org,direct
set GOROOT=C:\Users\Anwender\go\pkg\mod\golang.org\toolchain@v0.0.1-go1.24.2.windows-amd64
set GOSUMDB=sum.golang.org
set GOTELEMETRY=local
set GOTELEMETRYDIR=C:\Users\Anwender\AppData\Roaming\go\telemetry
set GOTMPDIR=
set GOTOOLCHAIN=auto
set GOTOOLDIR=C:\Users\Anwender\go\pkg\mod\golang.org\toolchain@v0.0.1-go1.24.2.windows-amd64\pkg\tool\windows_amd64
set GOVCS=
set GOVERSION=go1.24.2
set GOWORK=
set PKG_CONFIG=pkg-config

What did you do?

I am currently refactoring a project to use generics and at some point the go compiler stopped working.

What did you see happen?

The compiler deadlocks with the following message:

# github.com/lumaraf/sudoku-solver/restriction
fatal error: all goroutines are asleep - deadlock!

goroutine 1 [sync.Mutex.Lock]:
internal/sync.runtime_SemacquireMutex(0x2?, 0xf7?, 0xc00014a028?)
	runtime/sema.go:95 +0x25
internal/sync.(*Mutex).lockSlow(0xc0004d84f8)
	internal/sync/mutex.go:149 +0x15d
internal/sync.(*Mutex).Lock(...)
	internal/sync/mutex.go:70
sync.(*Mutex).Lock(...)
	sync/mutex.go:46
cmd/compile/internal/types2.(*Named).resolve(0xc0004d84d0)
	cmd/compile/internal/types2/named.go:176 +0x5f
cmd/compile/internal/types2.(*Named).TypeParams(...)
	cmd/compile/internal/types2/named.go:322
cmd/compile/internal/types2.(*subster).typ(0xc00014a798, {0x1b7c168, 0xc0004e5880})
	cmd/compile/internal/types2/subst.go:245 +0x82b
cmd/compile/internal/types2.(*subster).var_(0xc00014a5d8?, 0xc0004e58f0)
	cmd/compile/internal/types2/subst.go:288 +0x2c
cmd/compile/internal/types2.substList[...](...)
	cmd/compile/internal/types2/subst.go:317
cmd/compile/internal/types2.(*subster).tuple(0x21df1b25718?, 0xc00040cae0)
	cmd/compile/internal/types2/subst.go:304 +0xa3
cmd/compile/internal/types2.(*subster).typ(0xc00014a798, {0x1b7c140, 0xc0004e2c00})
	cmd/compile/internal/types2/subst.go:164 +0x44a
cmd/compile/internal/types2.(*Checker).subst(0x0, {0x0?, 0x0?, 0x0?}, {0x1b7c140, 0xc0004e2c00}, 0xc0004f0000, 0x0, 0xc00041e260)
	cmd/compile/internal/types2/subst.go:78 +0x1ac
cmd/compile/internal/types2.(*Checker).newAliasInstance(0x0, {0x0?, 0x45349b?, 0xc0?}, 0xc0004e2c40, {0xc00041ede0, 0x2, 0x2}, 0x0, 0xc00041e260)
	cmd/compile/internal/types2/alias.go:165 +0x1c5
cmd/compile/internal/types2.(*Checker).instance(0x0, {0x0, 0x0, 0x0}, {0x1b7d910, 0xc0004e2c40}, {0xc00041ede0, 0x2, 0x2}, 0x0, ...)
	cmd/compile/internal/types2/instantiate.go:150 +0x4b0
cmd/compile/internal/types2.Instantiate(0xc00041e260, {0x1b7c190, 0xc0004e2c40}, {0xc00041ede0, 0x2, 0x2}, 0x0)
	cmd/compile/internal/types2/instantiate.go:70 +0x326
cmd/compile/internal/importer.(*reader).doTyp(0xc00014abd0)
	cmd/compile/internal/importer/ureader.go:258 +0xcc
cmd/compile/internal/importer.(*pkgReader).typIdx(0xc00047c0e0, {0x47c0e0?, 0xc0?}, 0xc0004d4ba0)
	cmd/compile/internal/importer/ureader.go:231 +0x18e
cmd/compile/internal/importer.(*reader).typ(0xc00014adf8)
	cmd/compile/internal/importer/ureader.go:201 +0x68
cmd/compile/internal/importer.(*reader).doTyp(0xc00014adf8)
	cmd/compile/internal/importer/ureader.go:279 +0x15b
cmd/compile/internal/importer.(*pkgReader).typIdx(0xc00047c0e0, {0x47c0e0?, 0xc0?}, 0xc0004d4ba0)
	cmd/compile/internal/importer/ureader.go:231 +0x18e
cmd/compile/internal/importer.(*reader).typ(0xc00014b1e0)
	cmd/compile/internal/importer/ureader.go:201 +0x68
cmd/compile/internal/importer.(*reader).param(0xc00014b1e0)
	cmd/compile/internal/importer/ureader.go:365 +0x65
cmd/compile/internal/importer.(*reader).params(0xc00014b1e0)
	cmd/compile/internal/importer/ureader.go:355 +0x74
cmd/compile/internal/importer.(*reader).signature(0xc00014b1e0, 0x0, {0x0, 0x0, 0x0}, {0x0, 0x0, 0x0})
	cmd/compile/internal/importer/ureader.go:344 +0x65
cmd/compile/internal/importer.(*reader).interfaceType(0xc00014b1e0)
	cmd/compile/internal/importer/ureader.go:326 +0x16f
cmd/compile/internal/importer.(*reader).doTyp(0xc00014b1e0)
	cmd/compile/internal/importer/ureader.go:283 +0x3c5
cmd/compile/internal/importer.(*pkgReader).typIdx(0xc00047c0e0, {0x410480?, 0xc0?}, 0xc0004d4ba0)
	cmd/compile/internal/importer/ureader.go:231 +0x18e
cmd/compile/internal/importer.(*reader).typ(0xc0004d4c00)
	cmd/compile/internal/importer/ureader.go:201 +0x68
cmd/compile/internal/importer.ReadPackage.(*pkgReader).objIdx.func1.1(0x2?)
	cmd/compile/internal/importer/ureader.go:450 +0x3e
cmd/compile/internal/types2.(*Named).resolve(0xc0004d84d0)
	cmd/compile/internal/types2/named.go:215 +0xf7
cmd/compile/internal/types2.(*Named).TypeParams(...)
	cmd/compile/internal/types2/named.go:322
cmd/compile/internal/types2.(*subster).typ(0xc00014be30, {0x1b7c168, 0xc0004d8540})
	cmd/compile/internal/types2/subst.go:245 +0x82b
cmd/compile/internal/types2.(*subster).var_(0x196dc20?, 0xc0004d85b0)
	cmd/compile/internal/types2/subst.go:288 +0x2c
cmd/compile/internal/types2.substList[...](...)
	cmd/compile/internal/types2/subst.go:317
cmd/compile/internal/types2.(*subster).tuple(0x195f420?, 0xc00040c4f8)
	cmd/compile/internal/types2/subst.go:304 +0xa3
cmd/compile/internal/types2.(*subster).typ(0xc00014be30, {0x1b7c140, 0xc0004cfac0})
	cmd/compile/internal/types2/subst.go:165 +0x46b
cmd/compile/internal/types2.(*subster).func_(0xc000415900?, 0xc0004d8620)
	cmd/compile/internal/types2/subst.go:331 +0x2c
cmd/compile/internal/types2.substList[...](...)
	cmd/compile/internal/types2/subst.go:317
cmd/compile/internal/types2.(*subster).typ(0xc00014be30, {0x1b7c1e0, 0xc0004158b0})
	cmd/compile/internal/types2/subst.go:188 +0x9fa
cmd/compile/internal/types2.(*Checker).subst(0xc000430000, {0xc000400000?, 0x41ea60?, 0xc0?}, {0x1b7c1e0, 0xc0004158b0}, 0xc0004d14a0, 0xc0004d93b0, 0xc00041e260)
	cmd/compile/internal/types2/subst.go:78 +0x1ac
cmd/compile/internal/types2.(*Named).expandUnderlying(0xc0004d93b0)
	cmd/compile/internal/types2/named.go:670 +0x4e9
cmd/compile/internal/types2.(*Named).resolve(0xc0004d93b0)
	cmd/compile/internal/types2/named.go:189 +0x154
cmd/compile/internal/types2.(*Named).TypeParams(0x2142fb0?)
	cmd/compile/internal/types2/named.go:322 +0x13
cmd/compile/internal/types2.(*Checker).instantiatedType.func3()
	cmd/compile/internal/types2/typexpr.go:490 +0x154
cmd/compile/internal/types2.(*Checker).processDelayed(0xc000430000, 0x8)
	cmd/compile/internal/types2/check.go:525 +0x211
cmd/compile/internal/types2.(*Checker).stmt(0xc000430000, 0x0, {0x1b7ddd0, 0xc00041e020})
	cmd/compile/internal/types2/stmt.go:707 +0x130a
cmd/compile/internal/types2.(*Checker).stmtList(0xc000430000, 0x0, {0xc0004080b0?, 0xc0004d05d0?, 0x500000048?})
	cmd/compile/internal/types2/stmt.go:122 +0x85
cmd/compile/internal/types2.(*Checker).funcBody(0xc000430000, 0xc0004100c0?, {0xc000412010?, 0x26ca7f1667856fc?}, 0xc0004cec00, 0xc000418040, {0x0?, 0x0?})
	cmd/compile/internal/types2/stmt.go:42 +0x310
cmd/compile/internal/types2.(*Checker).objDecl.(*Checker).funcDecl.func4()
	cmd/compile/internal/types2/decl.go:775 +0x3a
cmd/compile/internal/types2.(*Checker).processDelayed(0xc000430000, 0x0)
	cmd/compile/internal/types2/check.go:525 +0x211
cmd/compile/internal/types2.(*Checker).checkFiles(0xc000430000, {0xc0004080c0?, 0xc000080008?, 0xc000080558?})
	cmd/compile/internal/types2/check.go:467 +0x814
cmd/compile/internal/types2.(*Checker).Files(0xc00001c600?, {0xc0004080c0?, 0x0?, 0x0?})
	cmd/compile/internal/types2/check.go:427 +0x75
cmd/compile/internal/types2.(*Config).Check(0xc00041a1c0, {0xc00001c600?, 0xc00000a3e0?}, {0xc0004080c0, 0x2, 0x2}, 0xc000410360)
	cmd/compile/internal/types2/api.go:488 +0x19d
cmd/compile/internal/noder.checkFiles({0x0, {0x0, 0x0}}, {0xc000037300, 0x2, 0x199e7a0?})
	cmd/compile/internal/noder/irgen.go:95 +0x5c9
cmd/compile/internal/noder.writePkgStub({0x0?, {0x0?, 0x0?}}, {0xc000037300, 0x2, 0x2})
	cmd/compile/internal/noder/unified.go:319 +0x6a
cmd/compile/internal/noder.unified({0x0?, {0x0?, 0x0?}}, {0xc000037300?, 0x19191e0?, 0x0?})
	cmd/compile/internal/noder/unified.go:195 +0xb3
cmd/compile/internal/noder.LoadPackage({0xc00010c120, 0x2, 0xe})
	cmd/compile/internal/noder/noder.go:77 +0x43a
cmd/compile/internal/gc.Main(0x1a39ac8)
	cmd/compile/internal/gc/main.go:208 +0xcc5
main.main()
	cmd/compile/main.go:57 +0xf9

What did you expect to see?

My program or an error what is wrong in my code.

[randall77]

Might this be #63285?

[cagedmantis]

@Lumaraf Can you provide a snippet that reproduces the problem?

[Lumaraf]

So far i was unable to reproduce the error with a simple example. With the extra information from #63285 i was able to identify some pieces of my code that are involved in trigger the error. I managed to refactor my code to work around the bug. The loop of parametric types is still there, but now with an extra type involved which seems to help.