posix_spawn: parent can get stuck in uninterruptible sleep if child receives SIGTSTP early enough

[Adhemerval Zanella Netto]

On 13/09/22 07:04, Florian Weimer wrote:
> * Adhemerval Zanella Netto:
> 
>> On 22/08/22 15:21, Florian Weimer wrote:
>>> * Adhemerval Zanella Netto via Libc-help:
>>>
>>>> Right, my mistake.  I understood the issue better now, although I am
>>>> still puzzled why SIGTSTP is only being triggered on sigprocmask (sing
>>>> default action is still to stop PROCESS).
>>>
>>> I think it's a maskable stop, not an unmaskable one, like SIGSTOP.
>>
>> Yeah, we do block the signal on parent (internal_signal_block_all). 
>>
>>>
>>> This looks a vfork-specific bug that can't happen with fork.  I don't
>>> see how to fix it in a generic fashion because we can't unblock SIGTSTP
>>> and launch the new process in an atomic fashion.
>>
>> We might ask for a new clone3 field to define the default signal mask on 
>> process start (and thus omit the final sigprocmask before execve).
> 
> It might already possible to fix this using io_uring.  Unfortunately, I
> didn't attend the LPC presentation.

Is there anything that prevents to avoid using CLONE_VFORK? The code already
uses a allocated stack and do synchronizes with waitpid.