linux-kernel - Re: [PATCH v2] signal: add procfd

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Message-ID: <7D934AED-82E4-4DC3-8CCB-973680316B60@brauner.io>
Date:   Sat, 01 Dec 2018 14:25:10 +1300
From:   Christian Brauner <christian@...uner.io>
To:     Arnd Bergmann <arnd@...db.de>
CC:     Andy Lutomirski <luto@...capital.net>,
        Andy Lutomirski <luto@...nel.org>,
        Florian Weimer <fweimer@...hat.com>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Serge E. Hallyn" <serge@...lyn.com>, Jann Horn <jannh@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>, cyphar@...har.com,
        Al Viro <viro@...iv.linux.org.uk>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Daniel Colascione <dancol@...gle.com>,
        Tim Murray <timmurray@...gle.com>, linux-man@...r.kernel.org,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH v2] signal: add procfd_signal() syscall

On November 30, 2018 10:40:49 AM GMT+13:00, Arnd Bergmann <arnd@...db.de> wrote:
>On Thu, Nov 29, 2018 at 10:35 PM Christian Brauner
><christian@...uner.io> wrote:
>> On Thu, Nov 29, 2018 at 10:02:13PM +0100, Arnd Bergmann wrote:
>> > On Thu, Nov 29, 2018 at 9:14 PM Andy Lutomirski
><luto@...capital.net> wrote:
>> >
>> > Is the current procfd_signal() proposal (under whichever name)
>sufficient
>> > to correctly implement both sys_rt_sigqueueinfo() and
>sys_rt_tgsigqueueinfo()?
>>
>> Yes, I see no reason why not. My idea is to extend it - after we have
>a
>> basic version in - to also work with:
>> /proc/<pid>/task/<tid>
>> If I'm not mistaken this should be sufficient to get
>rt_tgsigqueueinfo.
>> The thread will be uniquely identified by the tid descriptor and no
>> combination of /proc/<pid> and /proc/<pid>/task/<tid> is needed. Does
>> that sound reasonable?
>
>Yes. So it would currently replace rt_gsigqueueinfo() but
>not rt_tgsigqueueinfo(), and could be extended to do both
>afterwards, without making the interface ugly in any form?

Yes. :)

>
>I suppose we can always add more flags if needed, and you
>already ensure that flags is zero for the moment.

Yep.

>
>> > Can we implement sys_rt_sigtimedwait() based on signalfd()?
>> >
>> > If yes, that would leave waitid(), which already needs a
>replacement
>> > for y2038, and that should then also return a signalfd_siginfo.
>> > My current preference for waitid() would be to do a version that
>> > closely resembles the current interface, but takes a
>signalfd_siginfo
>> > and a __kernel_timespec based rusage replacement (possibly
>> > two of them to let us map wait6), but does not operate on procfd or
>> > take a signal mask. That would require yet another syscall, but I
>> > don't think I can do that before we want to have the set of y2038
>> > safe syscalls.
>>
>> All sounds reasonable to me but that's not a blocker for the current
>> syscall though, is it?
>
>I'd like to at least understand about sys_rt_sigtimedwait() before
>we go on, so we all know what's coming, and document the
>plans in the changelog.
>
>waitid() probably remains on my plate anyway, and I hope understand
>where we're at with it.
>
>     Arnd