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Subject: Re: [PATCH 0/2] Don't show PF_IO_WORKER in /proc/<pid>/task/
To:     Oleg Nesterov <oleg@redhat.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        io-uring <io-uring@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Stefan Metzmacher <metze@samba.org>
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 <m1zgyr2ddh.fsf@fess.ebiederm.org> <20210325204014.GD28349@redhat.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <70232822-ced2-30e8-f880-8ebadacc9cc2@kernel.dk>
Date:   Thu, 25 Mar 2021 14:43:20 -0600
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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