linux-kernel - Re: [PATCH] printk: remove unneeded dead-store assignment

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Message-ID: <20201106125749.GU20201@alley>
Date:   Fri, 6 Nov 2020 13:57:49 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Lukas Bulwahn <lukas.bulwahn@...il.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        John Ogness <john.ogness@...utronix.de>,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com,
        kernel-janitors@...r.kernel.org, linux-safety@...ts.elisa.tech
Subject: Re: [PATCH] printk: remove unneeded dead-store assignment

On Fri 2020-11-06 04:40:05, Lukas Bulwahn wrote:
> make clang-analyzer on x86_64 defconfig caught my attention with:
> 
>   kernel/printk/printk_ringbuffer.c:885:3: warning:
>   Value stored to 'desc' is never read [clang-analyzer-deadcode.DeadStores]
>                 desc = to_desc(desc_ring, head_id);
>                 ^
> 
> Commit b6cf8b3f3312 ("printk: add lockless ringbuffer") introduced
> desc_reserve() with this unneeded dead-store assignment.
> 
> As discussed with John Ogness privately, this is probably just some minor
> left-over from previous iterations of the ringbuffer implementation. So,
> simply remove this unneeded dead assignment to make clang-analyzer happy.
> 
> 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>

The patch is committed in printk/linux.git, branch for-5.10-trivial.

It might still go into 5.10 when there is another important fix.
Otherwise, it would need to wait for 5.11 merge window.

Best Regards,
Petr