Re: [PATCH 12/23] nptl: Introduce __nptl_deferred_init

[Florian Weimer <fweimer@redhat.com>]

* Adhemerval Zanella:

> On 12/05/2021 13:58, Florian Weimer via Libc-alpha wrote:
>> This function is called once by pthread_create, before spawning
>> the first thread, and also within pthread_cancel.  Since it sets up
>> cancellation handlers, place it along with the pthread_cancel
>> implementation within libc.
>
> Why does it need to be initialized by pthread_create as well?  I think
> moving the initialization to pthread_cancel and only setting once
> when pthread_cancel is called (and not tying to __libc_single_threaded)
> is slight better since it avoids the setup of SIGCANCEL for programs
> that do not use cancellation.

We need to unblock SIGCANCEL anyway, so that we can send the signal.
This part can't be deferred until pthread_cancel is called.

We could delay installing the SIGCANCEL handler because it's a global
resource, assuming that unshare (CLONE_SIGHAND) will fail in the kernel.

> Also, it seems wrong that pthread_cancel.c it the implementation
> that setups both SIGCANCEL and SIGSETXID.  It also seems wrong
> the rt_sigprocmask, SIG_UNBLOCK for pthread_cancel.

Hmm.  Should we have separate initialization functions then?

> I think it would be better to just setup the SIGCANCEL on pthread_cancel.c
> and move the the SIGSETXID to nptl/nptl_setxid.c.

As I said, we have to unblock SIGCANCEL as part of pthread_create anyway
(for both the old and the new thread).

Thanks,
Florian