linux-kernel - Re: [RFC PATCH 04/13] vfio/mdev: remove the usage of the list iterator after the loop

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Message-ID: <CAHk-=whpK93+mF8CPJZo0KxDeHrV2GL05=HT7=y+GnhcNbNyUA@mail.gmail.com>
Date:   Wed, 23 Feb 2022 12:34:18 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Jason Gunthorpe <jgg@...pe.ca>, Jakob <jakobkoschel@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Arnd Bergman <arnd@...db.de>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Mike Rapoport <rppt@...nel.org>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Brian Johannesmeyer <bjohannesmeyer@...il.com>,
        Cristiano Giuffrida <c.giuffrida@...nl>,
        "Bos, H.J." <h.j.bos@...nl>
Subject: Re: [RFC PATCH 04/13] vfio/mdev: remove the usage of the list
 iterator after the loop

On Wed, Feb 23, 2022 at 12:19 PM Rasmus Villemoes
<linux@...musvillemoes.dk> wrote:
>
> I have often wished that the iterator macros would consistently set the
> loop variable to NULL upon reaching the end.

I really think the rule should be that to a 99% approximation, we
should strive only ever use the iterated-upon value *inside* the loop.

No, that's now how we do it now. But I think the "break out and do the
work outside the loop" case is kind of broken anyway. It makes you
test the condition twice - and while a compiler might be smart enough
to optimize the second test away, it's still just plain ugly.

             Linus