macOS: sleep builtin freezes after suspending

[McDutchie]

Steps to reproduce:

1. sleep 3
2. press Ctrl+Z before it finishes (sleep builtin is forked into its own process and suspended)
3. fg

sleep should resume and terminate, but instead, the forked sleep builtin freezes, consuming 100% CPU. Only SIGKILL (kill -9) will terminate it, although it can still be suspended again.

This is reproducible on (at least) macOS 12.7.6 arm64. I can also reproduce this on 93u+ 2012-08-01 and on ksh2020.

[McDutchie]

I suspect this is a bug in macOS.

@posguy99, can you reproduce this on a later macOS version?

[posguy99]

Yes, Ventura 13.7.2 on arm64.

$ sw_vers
ProductName:		macOS
ProductVersion:		13.7.2
BuildVersion:		22H313
$ sleep 3
^Z[1] + Stopped                  sleep 3
$ fg
sleep 3

And the shell process is stuck at 100% CPU afterwards according to Activity Monitor.

[posguy99]

Doesn't happen on a Debian x86 VM.

[posguy99]

Here's a different behavior. Same macOS version, this is x64 vs arm64.

$ sw_vers
ProductName:		macOS
ProductVersion:		13.7.2
BuildVersion:		22H313
$ sleep 3
^Z[1] + Stopped                  sleep 3
$ fg
sleep 3
Illegal instruction
$ 

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