linux-kernel - Re: [PATCH] srcu: drop the needless initialization in srcu_gp

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Message-ID: <CAKXUXMy7TqCZjVMKwiQJj5bYUDpdGZE2hhbB2WfSA2AX1hM=zQ@mail.gmail.com>
Date:   Tue, 15 Mar 2022 18:04:41 +0100
From:   Lukas Bulwahn <lukas.bulwahn@...il.com>
To:     Paul McKenny <paulmck@...nel.org>
Cc:     rcu@...r.kernel.org, Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        kernel-janitors <kernel-janitors@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] srcu: drop the needless initialization in srcu_gp_start()

On Tue, Mar 15, 2022 at 5:52 PM Paul E. McKenney <paulmck@...nel.org> wrote:
>
> On Tue, Mar 15, 2022 at 09:55:49AM +0100, Lukas Bulwahn wrote:
> > Commit 9c7ef4c30f12 ("srcu: Make Tree SRCU able to operate without snp_node
> > array") initializes the local variable sdp differently depending on the
> > srcu's state in srcu_gp_start().
> >
> > Hence, the initialization of sdp with the variable definition is not used
> > before its second initialization.
> >
> > Drop the needless initialization in srcu_gp_start() to have clear code.
> >
> > No functional change. Some changes in the resulting object code due to
> > various rearrangements by the compiler.
> >
> > Signed-off-by: Lukas Bulwahn <lukas.bulwahn@...il.com>
> > ---
> > Paul, please pick this minor non-urgent clean-up patch.
>
> Good eyes, thank you!
>
> I have pulled this in for testing and review.  If things go will,
> I expect to push it into the v5.19 merge window (that is, not the one
> that will likely open next week, but the one after that).
>
> As usual, I could not resist wordsmithing the commit log.  Could you
> please check out the wordsmithed version below to make sure that I did
> not mess something up?
>

Wordsmithing was good. I am basically still reading in your versions
what I intended to state with my commit message; +1!

And of course, you are a native speaker; so, I trust your English is
better than mine.

Lukas

>                                                         Thanx, Paul
>
> ------------------------------------------------------------------------
>
> commit a0c59d99e87c52d6832e1ad39421b4a4386cdfd6
> Author: Lukas Bulwahn <lukas.bulwahn@...il.com>
> Date:   Tue Mar 15 09:55:49 2022 +0100
>
>     srcu: Drop needless initialization of sdp in srcu_gp_start()
>
>     Commit 9c7ef4c30f12 ("srcu: Make Tree SRCU able to operate without
>     snp_node array") initializes the local variable sdp differently depending
>     on the srcu's state in srcu_gp_start().  Either way, this initialization
>     overwrites the value used when sdp is defined.
>
>     This commit therefore drops this pointless definition-time initialization.
>     Although there is no functional change, compiler code generation may
>     be affected.
>
>     Signed-off-by: Lukas Bulwahn <lukas.bulwahn@...il.com>
>     Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
>
> diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> index e78b1c7929d6..3bc8267c5d0b 100644
> --- a/kernel/rcu/srcutree.c
> +++ b/kernel/rcu/srcutree.c
> @@ -609,7 +609,7 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock);
>   */
>  static void srcu_gp_start(struct srcu_struct *ssp)
>  {
> -       struct srcu_data *sdp = this_cpu_ptr(ssp->sda);
> +       struct srcu_data *sdp;
>         int state;
>
>         if (smp_load_acquire(&ssp->srcu_size_state) < SRCU_SIZE_WAIT_BARRIER)