linux-kernel - Re: [RFC PATCH v1 07/25] printk-rb: add functionality required by printk

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Date:   Tue, 12 Feb 2019 09:15:36 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Daniel Wang <wonderfly@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        Jiri Slaby <jslaby@...e.com>,
        Peter Feiner <pfeiner@...gle.com>,
        linux-serial@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [RFC PATCH v1 07/25] printk-rb: add functionality required by printk

On Tue, Feb 12, 2019 at 6:30 AM John Ogness <john.ogness@...utronix.de> wrote:
>
> +                       while (atomic_long_read(&rb->lost)) {
> +                               atomic_long_dec(&rb->lost);
> +                               rb->seq++;
> +                       }

This looks like crazy garbage. It's neither atomic nor sane.

Why isn't it something like

    if (atomic_long_read(&rb->lost)) {
        long lost = atomic_xchg(&rb->lost, 0);
        rb->seq += lost;
    }

instead?

                Linus