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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu, 25 Mar 2021 15:37:39 -0700
Message-ID: <CAHk-=wgmHRvoYdsA2ZL4aEOYvNx-5c7typsUbFcqq+GmOMcoDQ@mail.gmail.com>
Subject: Re: [PATCH 0/2] Don't show PF_IO_WORKER in /proc/<pid>/task/
To:     Jens Axboe <axboe@kernel.dk>
Cc:     "Eric W. Biederman" <ebiederm@xmission.com>,
        io-uring <io-uring@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Oleg Nesterov <oleg@redhat.com>,
        Stefan Metzmacher <metze@samba.org>
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On Thu, Mar 25, 2021 at 2:44 PM Jens Axboe <axboe@kernel.dk> wrote:
>
> In the spirit of "let's just try it", I ran with the below patch. With
> that, I can gdb attach just fine to a test case that creates an io_uring
> and a regular thread with pthread_create(). The regular thread uses
> the ring, so you end up with two iou-mgr threads. Attach:
>
> [root@archlinux ~]# gdb -p 360
> [snip gdb noise]
> Attaching to process 360
> [New LWP 361]
> [New LWP 362]
> [New LWP 363]
[..]

Looks fairly sane to me.

I think this ends up being the right approach - just the final part
(famous last words) of "io_uring threads act like normal threads".

Doing it for VM and FS got rid of all the special cases there, and now
doing it for signal handling gets rid of all these ptrace etc issues.

And the fact that a noticeable part of the patch was removing the
PF_IO_WORKER tests again looks like a very good sign to me.

In fact, I think you could now remove all the freezer hacks too -
because get_signal() will now do the proper try_to_freeze(), so all
those freezer things are stale as well.

Yeah, it's still going to be different in that there's no real user
space return, and so it will never look _entirely_ like a normal
thread, but on the whole I really like how this does seem to get rid
of another batch of special cases.

               Linus