linux-kernel - Re: [PATCH] io_thread/x86: don't reset 'cs', 'ss', 'ds' and 'es' registers for io

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Message-ID: <CAHk-=wj+njBWpgFqueHMVk1U8-APxZsgRsrOvhybcBEjspzGSg@mail.gmail.com>
Date:   Mon, 3 May 2021 16:19:35 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Andy Lutomirski <luto@...nel.org>, Jens Axboe <axboe@...nel.dk>,
        Stefan Metzmacher <metze@...ba.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        io-uring <io-uring@...r.kernel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: [PATCH] io_thread/x86: don't reset 'cs', 'ss', 'ds' and 'es'
 registers for io_threads

On Mon, May 3, 2021 at 4:16 PM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> These days they really are fully regular user threads, they just don't
> return to user space because they continue to do the IO work that they
> were created for.

IOW, you should think of them as "io_uring does an interface clone()
to generate an async thread, it does the work and then exits".

Now, that's the conceptual thing - in reality one thread can do
multiple async things - but it's the mental image you should have.

Don't think of them as kernel threads. Yes, that's how it started, but
that really ended up being very very painful indeed.

            Linus