linux-kernel - Re: [PATCH RESEND] taskstats: remove unneeded dead assignment

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Date:   Tue, 28 Dec 2021 11:39:19 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Lukas Bulwahn <lukas.bulwahn@...il.com>
Cc:     Balbir Singh <bsingharora@...il.com>, Tom Rix <trix@...hat.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        clang-built-linux@...glegroups.com,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RESEND] taskstats: remove unneeded dead assignment

On Mon, Dec 27, 2021 at 5:10 AM Lukas Bulwahn <lukas.bulwahn@...il.com> wrote:
>
> make clang-analyzer on x86_64 defconfig caught my attention with:
>
>   kernel/taskstats.c:120:2: warning: Value stored to 'rc' is never read \
>   [clang-analyzer-deadcode.DeadStores]
>           rc = 0;
>           ^
>
> Commit d94a041519f3 ("taskstats: free skb, avoid returns in
> send_cpu_listeners") made send_cpu_listeners() not return a value and
> hence, the rc variable remained only to be used within the loop where
> it is always assigned before read and it does not need any other
> initialisation.
>
> So, simply remove this unneeded dead initializing assignment.
>
> As compilers will detect this unneeded assignment and optimize this anyway,
> the resulting object code is identical before and after this change.
>
> No functional change. No change to object code.
>
> Signed-off-by: Lukas Bulwahn <lukas.bulwahn@...il.com>

I was going to ask "what happens when the list is empty?" but `rc` is
only used in a loop where that's not the case. Thanks for the patch!

It looks like
commit d94a041519f3 ("[PATCH] taskstats: free skb, avoid returns in
send_cpu_listeners")
from v2.6.18-rc4
is what changed send_cpu_listeners not to use rc outside of the loop.

Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

> ---
> applies cleanly on current master and next-20201105
> Resend: still applies cleanly on next-20211224
>
> Balbir, please pick this minor non-urgent clean-up patch.
>
>  kernel/taskstats.c | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/kernel/taskstats.c b/kernel/taskstats.c
> index a2802b6ff4bb..bd18a7bf5276 100644
> --- a/kernel/taskstats.c
> +++ b/kernel/taskstats.c
> @@ -117,7 +117,6 @@ static void send_cpu_listeners(struct sk_buff *skb,
>
>         genlmsg_end(skb, reply);
>
> -       rc = 0;
>         down_read(&listeners->sem);
>         list_for_each_entry(s, &listeners->list, list) {
>                 skb_next = NULL;
> --
> 2.17.1
>


-- 
Thanks,
~Nick Desaulniers