syscall: apparent deadlock in `TestExecPtrace`

[gopherbot]

#!watchflakes
post <- pkg == "syscall" && log ~ `test timed out` && log ~ `\s+TestExecPtrace \(\d+m`

Issue created automatically to collect these failures.

Example (log):

panic: test timed out after 15m0s
running tests:
	TestExecPtrace (14m59s)

goroutine 44 gp=0x400018c000 m=7 mp=0x4000080708 [running]:
panic({0x14fe40?, 0x4000184050?})
	/home/gopher/build/go/src/runtime/panic.go:779 +0x140 fp=0x4000051f00 sp=0x4000051e50 pc=0x472c0
testing.(*M).startAlarm.func1()
	/home/gopher/build/go/src/testing/testing.go:2366 +0x30c fp=0x4000051fd0 sp=0x4000051f00 pc=0xec68c
runtime.goexit({})
...

goroutine 20 gp=0x400018c340 m=nil [GC worker (idle), 14 minutes]:
runtime.gopark(0x400003a7b0?, 0x0?, 0x0?, 0x0?, 0x0?)
	/home/gopher/build/go/src/runtime/proc.go:402 +0xc8 fp=0x400003a730 sp=0x400003a710 pc=0x4aad8
runtime.gcBgMarkWorker()
	/home/gopher/build/go/src/runtime/mgc.go:1310 +0xd8 fp=0x400003a7d0 sp=0x400003a730 pc=0x2ba18
runtime.goexit({})
	/home/gopher/build/go/src/runtime/asm_arm64.s:1222 +0x4 fp=0x400003a7d0 sp=0x400003a7d0 pc=0x823a4
created by runtime.gcBgMarkStartWorkers in goroutine 13
	/home/gopher/build/go/src/runtime/mgc.go:1234 +0x28

— watchflakes

[gopherbot]

Found new dashboard test flakes for:

#!watchflakes
default <- pkg == "syscall" && test == ""

2023-12-05 17:17 openbsd-arm64-jsing go@285ef16b syscall (log)

panic: test timed out after 15m0s
running tests:
	TestExecPtrace (14m59s)

goroutine 44 gp=0x400018c000 m=7 mp=0x4000080708 [running]:
panic({0x14fe40?, 0x4000184050?})
	/home/gopher/build/go/src/runtime/panic.go:779 +0x140 fp=0x4000051f00 sp=0x4000051e50 pc=0x472c0
testing.(*M).startAlarm.func1()
	/home/gopher/build/go/src/testing/testing.go:2366 +0x30c fp=0x4000051fd0 sp=0x4000051f00 pc=0xec68c
runtime.goexit({})
...

goroutine 20 gp=0x400018c340 m=nil [GC worker (idle), 14 minutes]:
runtime.gopark(0x400003a7b0?, 0x0?, 0x0?, 0x0?, 0x0?)
	/home/gopher/build/go/src/runtime/proc.go:402 +0xc8 fp=0x400003a730 sp=0x400003a710 pc=0x4aad8
runtime.gcBgMarkWorker()
	/home/gopher/build/go/src/runtime/mgc.go:1310 +0xd8 fp=0x400003a7d0 sp=0x400003a730 pc=0x2ba18
runtime.goexit({})
	/home/gopher/build/go/src/runtime/asm_arm64.s:1222 +0x4 fp=0x400003a7d0 sp=0x400003a7d0 pc=0x823a4
created by runtime.gcBgMarkStartWorkers in goroutine 13
	/home/gopher/build/go/src/runtime/mgc.go:1234 +0x28

— watchflakes

[bcmills]

(attn @golang/openbsd)

[gopherbot]

Found new dashboard test flakes for:

#!watchflakes
post <- pkg == "syscall" && log ~ `test timed out` && log ~ `\s+TestExecPtrace \(\d+m`

2023-12-15 21:57 openbsd-arm64-jsing go@79309716 syscall (log)

panic: test timed out after 15m0s
running tests:
	TestExecPtrace (14m59s)

goroutine 14 gp=0x4000083500 m=10 mp=0x4000081008 [running]:
panic({0x14ff20?, 0x4000098210?})
	/home/gopher/build/go/src/runtime/panic.go:779 +0x140 fp=0x4000053f00 sp=0x4000053e50 pc=0x47660
testing.(*M).startAlarm.func1()
	/home/gopher/build/go/src/testing/testing.go:2366 +0x30c fp=0x4000053fd0 sp=0x4000053f00 pc=0xece4c
runtime.goexit({})
...
syscall_test.TestExecPtrace(0x4000292820)
	/home/gopher/build/go/src/syscall/syscall_ptrace_test.go:30 +0xc4 fp=0x400004ff60 sp=0x400004fe90 pc=0x132704
testing.tRunner(0x4000292820, 0x18fd78)
	/home/gopher/build/go/src/testing/testing.go:1689 +0xec fp=0x400004ffb0 sp=0x400004ff60 pc=0xe922c
testing.(*T).Run.gowrap1()
	/home/gopher/build/go/src/testing/testing.go:1742 +0x2c fp=0x400004ffd0 sp=0x400004ffb0 pc=0xea07c
runtime.goexit({})
	/home/gopher/build/go/src/runtime/asm_arm64.s:1222 +0x4 fp=0x400004ffd0 sp=0x400004ffd0 pc=0x82b64
created by testing.(*T).Run in goroutine 1
	/home/gopher/build/go/src/testing/testing.go:1742 +0x318

— watchflakes