linux-kernel - Re: [PATCH next v4 1/5] minmax: Add umin(a, b) and umax(a, b)

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Message-ID: <737627fd-b68b-4c9d-8700-f0e0d6d9cec8@moroto.mountain>
Date: Fri, 12 Jan 2024 15:49:59 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: David Laight <David.Laight@...lab.com>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	'Andy Shevchenko' <andriy.shevchenko@...ux.intel.com>,
	'Andrew Morton' <akpm@...ux-foundation.org>,
	"'Matthew Wilcox (Oracle)'" <willy@...radead.org>,
	'Christoph Hellwig' <hch@...radead.org>,
	"'Jason A. Donenfeld'" <Jason@...c4.com>
Subject: Re: [PATCH next v4 1/5] minmax: Add umin(a, b) and umax(a, b)

On Mon, Sep 18, 2023 at 08:16:30AM +0000, David Laight wrote:
> +/**
> + * umin - return minimum of two non-negative values
> + *   Signed types are zero extended to match a larger unsigned type.
> + * @x: first value
> + * @y: second value
> + */
> +#define umin(x, y)	\
> +	__careful_cmp((x) + 0u + 0ul + 0ull, (y) + 0u + 0ul + 0ull, <)

Why do we match "a larger unsigned type" instead of ULL_MAX?  Presumably
it helps performance somehow...  I agree that it's probably fine but I
would be more comfortable if it skipped UINT_MAX and jumped directly to
ULONG_MAX.  These days 4 gigs is small potatoes.  The vmalloc() function
can allocate 4G so we've had integer overflow bugs with this before.

regards,
dan carpenter