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os/signal: Reset doesn't reset ignored signals #46321

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perillo opened this issue May 22, 2021 · 7 comments · May be fixed by #71708
Open

os/signal: Reset doesn't reset ignored signals #46321

perillo opened this issue May 22, 2021 · 7 comments · May be fixed by #71708
Labels
compiler/runtime Issues related to the Go compiler and/or runtime. NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
Milestone
Backlog

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@perillo
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perillo commented May 22, 2021

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

$ go version
go version go1.16.4 linux/amd64

Does this issue reproduce with the latest release?

Yes, including go1.17 devel

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

go env Output
$ go env
GO111MODULE="on"
GOARCH="amd64"
GOBIN="/home/manlio/.local/bin"
GOCACHE="/home/manlio/.cache/go-build"
GOENV="/home/manlio/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE="*.local"
GOMODCACHE="/home/manlio/.local/lib/go/pkg/mod"
GONOPROXY=""
GONOSUMDB="*.local"
GOOS="linux"
GOPATH="/home/manlio/.local/lib/go:/home/manlio/src/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/lib/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.16.4"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/dev/null"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build3881295983=/tmp/go-build -gno-record-gcc-switches"
GOROOT/bin/go version: go version go1.16.4 linux/amd64
GOROOT/bin/go tool compile -V: compile version go1.16.4
uname -sr: Linux 5.12.5-arch1-1
/usr/lib/libc.so.6: GNU C Library (GNU libc) release release version 2.33.
gdb --version: GNU gdb (GDB) 10.2

What did you do?

https://play.golang.org/p/vYlTzluIuBL

What did you expect to see?

The last line of the output being false

What did you see instead?

The last line is true.

See https://groups.google.com/g/golang-nuts/c/W5NNNC0h5Zc for a discussion.
Thanks to Brian Candler for the simplified example.
@perillo
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perillo commented May 22, 2021

https://golang.org/cl/3580 described signal.Reset as "ability to restore initial signal handlers".

@mknyszek mknyszek added this to the Backlog milestone May 24, 2021
@mknyszek mknyszek added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label May 24, 2021
@mknyszek
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CC @ianlancetaylor via https://dev.golang.org/owners

To be clear, Reset says it specifically undoes the effects of Notify (https://golang.org/pkg/os/signal/#Reset) but it does not mention Ignore. But it does also say "all signal handlers are reset," so I see your point. I worry that maybe this has been working this way long enough that we can't actually change it at this point.

@ianlancetaylor
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At a quick look Reset already undoes a call to Ignore, except that it fails to adjust the data checked by Ignored. If I'm right that just seems like a bug, with no serious compatibility issues.

@bluec0re
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bluec0re commented Jul 6, 2021 •
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According to my tests (and a real life bug) this is not just with syscall.Ignored:

https://play.golang.org/p/NQlbXjitE17

The last run of sleepAndKill should have a similar output to the first run. I can't use time.Now in the playground, otherwise a measured delay would show ~2s for the last 2 executions instead of only for the one SIGINT is ignored.

EDIT: this is particular bad as ignored signals are inherited by child processes, so unmasking them before forking the child doesn't work. This can lead to quite unexpected behavior, especially if default signals like SIGCHLD are masked.

@gopherbot gopherbot added the compiler/runtime Issues related to the Go compiler and/or runtime. label Jul 7, 2022
@mknyszek mknyszek moved this to Triage Backlog in Go Compiler / Runtime Jul 15, 2022
@Andriamanitra Andriamanitra mentioned this issue Oct 31, 2022
Closed
@gabyhelp gabyhelp mentioned this issue Nov 24, 2024
Open
@fmeum fmeum linked a pull request Feb 13, 2025 that will close this issue
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@gopherbot
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Change https://go.dev/cl/649155 mentions this issue: os/signal: Let Reset reset ignored signals

@fmeum
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fmeum commented Feb 14, 2025

I've been bitten by this a number of times now, which motivated me to look into it more. As @bluec0re mentioned, there appears to be now way to recover from a signal.Ignore(syscall.SIGCHLD) to the point where exec.Cmd will no longer be able to start subprocesses. Other signals, once ignored, will also be forwarded to child processes as ignored with no way to recover from that state (excluding cgo).

Would a fix for this be accepted, perhaps with an associated GODEBUG flag?

@ianlancetaylor
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Patches are always welcome. I don't see why this needs a GODEBUG flag. Thanks.

I see that you sent a patch which is currently marked as "work in progress". You can send it to me when it is ready for review. Thanks.

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Labels
compiler/runtime Issues related to the Go compiler and/or runtime. NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
Projects
Go Compiler / Runtime
Status: Triage Backlog
Milestone
Backlog
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os/signal: let Reset reset Ignored signals fmeum/go
6 participants
@bluec0re @mknyszek @ianlancetaylor @fmeum @perillo @gopherbot