linux-kernel - Re: [PATCH v4 3/6] sysctl: Warn when a clamped sysctl parameter is set out of range

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Date:   Mon, 12 Mar 2018 14:00:27 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Waiman Long <longman@...hat.com>
Cc:     "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Al Viro <viro@...iv.linux.org.uk>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v4 3/6] sysctl: Warn when a clamped sysctl parameter is
 set out of range

On Mon, 12 Mar 2018 16:15:41 -0400 Waiman Long <longman@...hat.com> wrote:

> Even with clamped sysctl parameters, it is still not that straight
> forward to figure out the exact range of those parameters. One may
> try to write extreme parameter values to see if they get clamped.
> To make it easier, a warning with the expected range will now be
> printed into the kernel ring buffer when a clamped sysctl parameter
> receives an out of range value.
> 
> The pr_warn_ratelimited() macro is used to limit the number of warning
> messages that can be printed within a given period of time.
> 
> ...
>
> +#ifdef pr_fmt
> +#undef pr_fmt
> +#endif
> +#define pr_fmt(fmt)	"sysctl: " fmt

Why is it necessary to undefine pr_fmt?  That's a somewhat unusual
thing to do.