Re: [PATCH] linux: Fallback to fork and exec for clone fail on posix_spawn (BZ#29115)

[Alexey Izbyshev <izbyshev@ispras.ru>]

On 2022-05-02 23:02, Adhemerval Zanella wrote:
> On 02/05/2022 16:54, Alexey Izbyshev wrote:
>> On 2022-05-02 22:42, Adhemerval Zanella wrote:
>>> On 02/05/2022 16:15, Alexey Izbyshev wrote:
>>>> On 2022-05-02 21:06, Adhemerval Zanella wrote:
>>>>> +      while (__write_nocancel (args->pipe[1], &ret, sizeof (ret)) 
>>>>> < 0);
>>>> 
>>>> If the parent is killed, write() will fail with EPIPE, so this loop 
>>>> will become infinite. Maybe check for EPIPE and break?
>>> 
>>> We block all signals (__libc_signal_block_all), so the parent will be
>>> only killed
>>> by signals that can no be caught (SIGKILL).  Same for SIGPIPE.
>> 
>> The parent can indeed only be killed by SIGKILL, or simply exit from 
>> another thread, but how exactly it dies doesn't matter. But signals 
>> are already unblocked at this point in the child, so if SIGPIPE was 
>> ignored in the parent, it's ignored now in the child and is unblocked, 
>> hence write() can fail with EPIPE.
>> 
> 
> Right, I was thinking in term of the CLONE_VFORK which is not the case. 
>  But
> now checking on the closefrom and the pipe file descriptor issue, it 
> seems
> it would be better to have the error code communicate through a shared 
> memory
> instead of a pipe.

How do you propose to wait until the child exec's if you use shared 
memory? Do you plan to use clone(CLONE_VFORK) (but without CLONE_VM)?

Alexey