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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Mon, 1 Apr 2019 10:32:41 -0700
Message-ID: <CAHk-=wgXsK1X=PUaHNT9V-h+v2maB1bLA0P3XHXBNRa0e299XQ@mail.gmail.com>
Subject: Re: [PATCH v2 0/5] pid: add pidfd_open()
To:     Daniel Colascione <dancol@google.com>
Cc:     Jonathan Kowalski <bl0pbl33p@gmail.com>,
        Aleksa Sarai <cyphar@cyphar.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Christian Brauner <christian@brauner.io>,
        Jann Horn <jannh@google.com>,
        Andrew Lutomirski <luto@kernel.org>,
        David Howells <dhowells@redhat.com>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        Linux API <linux-api@vger.kernel.org>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
        Kees Cook <keescook@chromium.org>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Michael Kerrisk-manpages <mtk.manpages@gmail.com>,
        "Dmitry V. Levin" <ldv@altlinux.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>,
        Nagarathnam Muthusamy <nagarathnam.muthusamy@oracle.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Joel Fernandes <joel@joelfernandes.org>
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On Mon, Apr 1, 2019 at 9:45 AM Daniel Colascione <dancol@google.com> wrote:
>
> But doesn't the CSIGNAL approach still require that libraries somehow
> coordinate which non-SIGCHLD signal they use?

Yes. As mentioned, this was seldom used.

In some cases it's ok, eg aio would just specify the signal in
sigev_signo (except it was never fleshed out to have sival_ptr etc
because nobody ever did it, afaik).

> (Signal coordination a separate problem, unfortunately.)

Yeah, in several cases you would just want to signal a handler
directly, not an index into handlers.

Anyway, I'm just saying that the whole "reap children" part is not
necessarily tied to the pidfd thing. And honestly, nobody ever does
anything like that anyway in practice, because of all the other issues
it causes that you'll hit.

                 Linus