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

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Message-ID: <70232822-ced2-30e8-f880-8ebadacc9cc2@kernel.dk>
Date:   Thu, 25 Mar 2021 14:43:20 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Oleg Nesterov <oleg@...hat.com>,
        "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>,
        Stefan Metzmacher <metze@...ba.org>
Subject: Re: [PATCH 0/2] Don't show PF_IO_WORKER in /proc/<pid>/task/

On 3/25/21 2:40 PM, Oleg Nesterov wrote:
> On 03/25, Eric W. Biederman wrote:
>>
>> 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.
> 
> may be,
> 
>> 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.
> 
> may be.
> 
> But I don't think we can blame gdb. The kernel changed the rules, and this
> broke gdb. IOW, I don't agree this is gdb bug.

Right, that's what I was getting at too - and it's likely not just gdb.
We have to ensure that we don't break this use case, which seems to
imply that we:

1) Just make it work, or
2) Make them hidden in such a way that gdb doesn't see them, but
   regular tooling does

#2 seems fraught with peril, and maybe not even possible.

-- 
Jens Axboe