linux-kernel - Re: [PATCH 0/2] Don't show PF_IO

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Message-ID: <003d6524-3852-7ec2-9d60-63ec43c50187@kernel.dk>
Date:   Thu, 25 Mar 2021 18:08:11 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        io-uring <io-uring@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Stefan Metzmacher <metze@...ba.org>
Subject: Re: [PATCH 0/2] Don't show PF_IO_WORKER in /proc/<pid>/task/

On 3/25/21 4:37 PM, Linus Torvalds wrote:
> On Thu, Mar 25, 2021 at 2:44 PM Jens Axboe <axboe@...nel.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@...hlinux ~]# 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