Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH 0/2] Don't show PF_IO_WORKER in /proc/<pid>/task/
To:     Linus Torvalds <torvalds@linux-foundation.org>
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>
References: <20210325164343.807498-1-axboe@kernel.dk>
 <m1ft0j3u5k.fsf@fess.ebiederm.org>
 <CAHk-=wjOXiEAjGLbn2mWRsxqpAYUPcwCj2x5WgEAh=gj+o0t4Q@mail.gmail.com>
 <CAHk-=wg1XpX=iAv=1HCUReMbEgeN5UogZ4_tbi+ehaHZG6d==g@mail.gmail.com>
 <CAHk-=wgUcVeaKhtBgJO3TfE69miJq-krtL8r_Wf_=LBTJw6WSg@mail.gmail.com>
 <ad21da2b-01ea-e77c-70b2-0401059e322b@kernel.dk>
 <f9bc0bac-2ad9-827e-7360-099e1e310df5@kernel.dk>
 <CAHk-=wgmHRvoYdsA2ZL4aEOYvNx-5c7typsUbFcqq+GmOMcoDQ@mail.gmail.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <003d6524-3852-7ec2-9d60-63ec43c50187@kernel.dk>
Date:   Thu, 25 Mar 2021 18:08:11 -0600
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.10.0
MIME-Version: 1.0
In-Reply-To: <CAHk-=wgmHRvoYdsA2ZL4aEOYvNx-5c7typsUbFcqq+GmOMcoDQ@mail.gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 3/25/21 4:37 PM, Linus Torvalds wrote:
> 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.

I agree, and in fact there are more PF_IO_WORKER checks that can go
too. The patch is just the bare minimum.

> 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.

Yep

> 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.

That's what makes me feel better too. I think was so hung up on the
"never take signals" that it just didn't occur to me to go this
route instead.

I'll send out a clean series.

-- 
Jens Axboe