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

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Message-ID: <m135wj0xj8.fsf@fess.ebiederm.org>
Date:   Thu, 25 Mar 2021 15:48:59 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Jens Axboe <axboe@...nel.dk>,
        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/

Oleg Nesterov <oleg@...hat.com> writes:

> 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.

My point would be it is not strictly a regression either.  It is gdb not
handling new functionality.

If we can be backwards compatible and make ptrace_attach work that is
preferable.  If we can't saying the handful of ptrace using applications
need an upgrade to support processes that use io_uring may be
acceptable.

I don't see any easy to implement path that is guaranteed to work.

Eric