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

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Message-ID: <27a54fc2-865a-d90b-2429-d91170be5873@kernel.dk>
Date:   Thu, 25 Mar 2021 14:42:19 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        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 2:21 PM, Eric W. Biederman wrote:
> Jens Axboe <axboe@...nel.dk> writes:
> 
>> On 3/25/21 1:42 PM, Linus Torvalds wrote:
>>> On Thu, Mar 25, 2021 at 12:38 PM Linus Torvalds
>>> <torvalds@...ux-foundation.org> wrote:
>>>>
>>>> I don't know what the gdb logic is, but maybe there's some other
>>>> option that makes gdb not react to them?
>>>
>>> .. maybe we could have a different name for them under the task/
>>> subdirectory, for example (not  just the pid)? Although that probably
>>> messes up 'ps' too..
>>
>> Heh, I can try, but my guess is that it would mess up _something_, if
>> not ps/top.
> 
> Hmm.
> 
> So looking quickly the flip side of the coin is gdb (and other
> debuggers) needs a way to know these threads are special, so it can know
> not to attach.
> 
> I suspect getting -EPERM (or possibly a different error code) when
> attempting attach is the right was to know that a thread is not
> available to be debugged.

But that's what's being returned right now, and gdb seemingly doesn't
really handle that. And even if it was just a gdb issue that could be
fixed it (it definitely is), I'd still greatly prefer not having to do
that. It just takes too long for packages to get updated in distros, and
it'd be years until it got fixed widely. Secondly, I'm even more worried
about cases that we haven't seen yet. I doubt that gdb is the only thing
that'd fall over, not expecting threads in there that it cannot attach
to.

-- 
Jens Axboe