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

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Message-ID: <m1lfab0xs9.fsf@fess.ebiederm.org>
Date:   Thu, 25 Mar 2021 15:43:34 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Jens Axboe <axboe@...nel.dk>, 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/

Linus Torvalds <torvalds@...ux-foundation.org> writes:

> On Thu, Mar 25, 2021 at 12:42 PM Linus Torvalds
> <torvalds@...ux-foundation.org> 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..
>
> Actually, maybe the right model is to simply make all the io threads
> take signals, and get rid of all the special cases.
>
> Sure, the signals will never be delivered to user space, but if we
>
>  - just made the thread loop do "get_signal()" when there are pending signals
>
>  - allowed ptrace_attach on them
>
> they'd look pretty much like regular threads that just never do the
> user-space part of signal handling.
>
> The whole "signals are very special for IO threads" thing has caused
> so many problems, that maybe the solution is simply to _not_ make them
> special?

The special case in check_kill_permission is certainly unnecessary.
Having the signal blocked is enough to prevent signal_pending() from
being true. 


The most straight forward thing I can see is to allow ptrace_attach and
to modify ptrace_check_attach to always return -ESRCH for io workers
unless ignore_state is set causing none of the other ptrace operations
to work.

That is what a long running in-kernel thread would do today so
user-space aka gdb may actually cope with it.


We might be able to support if io workers start supporting SIGSTOP but I
am not at all certain.

Eric