linux-kernel - Re: [PATCH v2 0/2] Lock and Pointer guards

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Message-ID: <xhsmhy1l5or9n.mognet@vschneid.remote.csb>
Date:   Tue, 30 May 2023 14:58:12 +0100
From:   Valentin Schneider <vschneid@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     keescook@...omium.org, gregkh@...uxfoundation.org,
        pbonzini@...hat.com, linux-kernel@...r.kernel.org,
        ojeda@...nel.org, ndesaulniers@...gle.com, mingo@...hat.com,
        will@...nel.org, longman@...hat.com, boqun.feng@...il.com,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, paulmck@...nel.org,
        frederic@...nel.org, quic_neeraju@...cinc.com,
        joel@...lfernandes.org, josh@...htriplett.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        rcu@...r.kernel.org, tj@...nel.org, tglx@...utronix.de
Subject: Re: [PATCH v2 0/2] Lock and Pointer guards

On 30/05/23 11:23, Peter Zijlstra wrote:
> On Sat, May 27, 2023 at 12:18:04PM -0700, Linus Torvalds wrote:
>
>
>> And it turns out that the above two trivial macros are actually quite
>> useful in themselves. You want to do an auto-cleanup version of
>> 'struct fd'? It's trivial:
>>
>>     /* Trivial "getfd()" wrapper */
>>     static inline void release_fd(struct fd *fd)
>>     { fdput(*fd); }
>>
>>     #define auto_getfd(name, n) \
>>         auto_release_name(struct fd, name, fdget(n), release_fd)
>>
>
>>  - I think the above is simpler and objectively better in every way
>> from the explicitly scoped thing
>
> Well, I think having that as a option would still be very nice.
>

IMO the explicit scoping can help with readability. It gives a clear visual
indication of where critical sections are, and you can break it up with a
scope + guards as in migrate_swap_stop() to stay at sane indentation
levels (with Python context managers, this would all be one scope).

I'd argue that for these, the scope/indentation is beneficial and not just
a byproduct. Even for longer functions like try_to_wake_up(), this works
out alright.

This obviously falls apart when dealing with too many guards
(e.g. copy_process()) or if the resulting indentation is nuts, but I concur
that keeping the explicit scope as an option would be nice.