linux-kernel - Re: [RFC PATCH v2 1/5] futex: Add futex_set

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Date:   Thu, 22 Sep 2016 23:31:19 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Waiman Long <Waiman.Long@....com>
cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Jonathan Corbet <corbet@....net>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, Davidlohr Bueso <dave@...olabs.net>,
        Jason Low <jason.low2@....com>,
        Scott J Norton <scott.norton@....com>,
        Douglas Hatch <doug.hatch@....com>
Subject: Re: [RFC PATCH v2 1/5] futex: Add futex_set_timer() helper
 function

On Tue, 20 Sep 2016, Waiman Long wrote:

Please be more careful of your subject lines. First thing I thought was
that you add a helper which is used in later patches to find out that you
actualy consolidate duplicated code. Something like:

  futex: Consolidate duplicated timer setup code

would have told me right away what this is about.

> This patch adds a new futex_set_timer() function to consolidate all

Please do not use: "This patch ...". We already know that this is a patch,
otherwise it would not be tagged [PATCH n/m] in the subject line.

See Documentation/SubmittingPatches ....

> the sleeping hrtime setup code.

Let me give you a hint:

1:  The code has three identical code copies to set up the futex timeout.

2:  Add a helper function and consolidate the call sites.

#1 tells precisely what the problem is
#2 tells precisely how it is solved

Can you see the difference?

> +/*
> + * Helper function to set the sleeping hrtimer.
> + */
> +static inline void futex_set_timer(ktime_t *time, struct hrtimer_sleeper **pto,
> +		struct hrtimer_sleeper *timeout, int flags, u64 range_ns)

Please use futex_setup_timer() as the function name. I was confused when I
read the other patch that you wanted to "set" the timer before entering
into the place which would actually need it.

> +{
> +	if (!time)
> +		return;
> +	*pto = timeout;

Please don't do that. That's a horrible coding style.

What's wrong with returning NULL or the timeout pointer and assign it to
"to" at the call site?

Thanks,

	tglx