linux-kernel - Re: [PATCH] [RFC] io_uring: warning about unused-but-set parameter

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Date:   Mon, 20 Sep 2021 13:18:58 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Jens Axboe <axboe@...nel.dk>,
        Pavel Begunkov <asml.silence@...il.com>,
        Arnd Bergmann <arnd@...db.de>, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [RFC] io_uring: warning about unused-but-set parameter

On Mon, Sep 20, 2021 at 02:13:44PM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> When enabling -Wunused warnings by building with W=1, I get an
> instance of the -Wunused-but-set-parameter warning in the io_uring code:
> 
> fs/io_uring.c: In function 'io_queue_async_work':
> fs/io_uring.c:1445:61: error: parameter 'locked' set but not used [-Werror=unused-but-set-parameter]
>  1445 | static void io_queue_async_work(struct io_kiocb *req, bool *locked)
>       |                                                       ~~~~~~^~~~~~
> 
> There are very few warnings of this type, so it would be nice to enable
> this by default and fix all the existing instances. I was almost
> done, but this was added recently as a precaution to prevent code
> from using the parameter, which could be done by either removing
> the initialization, or by adding a (fake) use of the variable, which
> I do here with the cast to void.

Please don't.  These warning are utterly stupid and should not be
enabled.  For anything that is a "method" of sorts (that is assigned
to a function pointer), unused argument are perfectly normal.