linux-kernel - Re: [PATCH v5 2/4] slab: Introduce kmalloc

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Message-ID: <202511241612.6CF90E9@keescook>
Date: Mon, 24 Nov 2025 16:29:52 -0800
From: Kees Cook <kees@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Vlastimil Babka <vbabka@...e.cz>, Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Hyeonggon Yoo <42.hyeyoo@...il.com>,
	"Gustavo A . R . Silva" <gustavoars@...nel.org>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>, Jann Horn <jannh@...gle.com>,
	Przemek Kitszel <przemyslaw.kitszel@...el.com>,
	Marco Elver <elver@...gle.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Sasha Levin <sashal@...nel.org>, linux-mm@...ck.org,
	Randy Dunlap <rdunlap@...radead.org>,
	Miguel Ojeda <ojeda@...nel.org>,
	Matthew Wilcox <willy@...radead.org>,
	Vegard Nossum <vegard.nossum@...cle.com>,
	Harry Yoo <harry.yoo@...cle.com>,
	Nathan Chancellor <nathan@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
	Jonathan Corbet <corbet@....net>, Jakub Kicinski <kuba@...nel.org>,
	Yafang Shao <laoar.shao@...il.com>,
	Tony Ambardar <tony.ambardar@...il.com>,
	Alexander Lobakin <aleksander.lobakin@...el.com>,
	Jan Hendrik Farr <kernel@...rr.cc>,
	Alexander Potapenko <glider@...gle.com>,
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
	linux-doc@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH v5 2/4] slab: Introduce kmalloc_obj() and family

On Mon, Nov 24, 2025 at 01:35:12PM -0800, Linus Torvalds wrote:
> Those macros are illegible. And 99% of all users DO NOT WANT ANY OF
> THAT COMPLEXITY.

Okay, I think you're saying "I don't want the common helpers to include
the infrastructure for supporting the ..._sz() variants"?

> So no. We're not doing *any* of that. You make it simple and targeted
> to the *common* case, of you don't do this at all. Because that
> over-designed mess that actually turned some users *less* readable,
> but one line shorter, was bad.

Fair enough. Looking at the treewide change I prepared[1], it's less
than 1% of those mechanical replacements:

$ git show f79ee96ad6a3 | grep -E 'k.*alloc_(objs?|flex)\(' | wc -l
17473
$ git show f79ee96ad6a3 | grep '_sz(' | wc -l
114

I'll respin without the _sz variants, and try to improve the flex stuff.

-Kees

[1] https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/commit/?h=dev/v6.18-rc6/alloc_obj/v5

-- 
Kees Cook