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

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Message-ID: <20220315165228.GD4285@paulmck-ThinkPad-P17-Gen-1>
Date:   Tue, 15 Mar 2022 09:52:28 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Lukas Bulwahn <lukas.bulwahn@...il.com>
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@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] srcu: drop the needless initialization in srcu_gp_start()

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?

							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)