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From: David Laight <david.laight.linux@gmail.com>
To: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Kees Cook <kees@kernel.org>, Vlastimil Babka <vbabka@suse.cz>,
	Jonathan Corbet <corbet@lwn.net>,
	Andrew Morton <akpm@linux-foundation.org>,
	Christoph Lameter <cl@gentwo.org>,
	David Rientjes <rientjes@google.com>,
	Roman Gushchin <roman.gushchin@linux.dev>,
	Harry Yoo <harry.yoo@oracle.com>,
	"Gustavo A. R. Silva" <gustavoars@kernel.org>,
	workflows@vger.kernel.org, linux-doc@vger.kernel.org,
	linux-mm@kvack.org, linux-hardening@vger.kernel.org,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Randy Dunlap <rdunlap@infradead.org>,
	Miguel Ojeda <ojeda@kernel.org>,
	Przemek Kitszel <przemyslaw.kitszel@intel.com>,
	Matthew Wilcox <willy@infradead.org>,
	John Hubbard <jhubbard@nvidia.com>, Joe Perches <joe@perches.com>,
	Christoph Lameter <cl@linux.com>, Marco Elver <elver@google.com>,
	Vegard Nossum <vegard.nossum@oracle.com>,
	Pekka Enberg <penberg@kernel.org>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	Bill Wendling <morbo@google.com>,
	Justin Stitt <justinstitt@google.com>,
	Jann Horn <jannh@google.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Sasha Levin <sashal@kernel.org>,
	Nathan Chancellor <nathan@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Nick Desaulniers <nick.desaulniers+lkml@gmail.com>,
	Jakub Kicinski <kuba@kernel.org>,
	Yafang Shao <laoar.shao@gmail.com>,
	Tony Ambardar <tony.ambardar@gmail.com>,
	Alexander Lobakin <aleksander.lobakin@intel.com>,
	Jan Hendrik Farr <kernel@jfarr.cc>,
	Alexander Potapenko <glider@google.com>,
	linux-kernel@vger.kernel.org, llvm@lists.linux.dev
Subject: Re: [PATCH v6 4/5] slab: Introduce kmalloc_flex() and family
Date: Tue, 24 Feb 2026 11:11:51 +0000	[thread overview]
Message-ID: <20260224111151.6154ce59@pumpkin> (raw)
In-Reply-To: <675ec547-dac8-465f-b3c9-a0f97c5bdef7@lucifer.local>

On Tue, 24 Feb 2026 10:26:36 +0000
Lorenzo Stoakes <lorenzo.stoakes@oracle.com> wrote:

> On Wed, Dec 03, 2025 at 03:30:34PM -0800, Kees Cook wrote:
...
> > +/**
> > + * __alloc_flex - Allocate an object that has a trailing flexible array
> > + * @KMALLOC: kmalloc wrapper function to use for allocation.
> > + * @GFP: GFP flags for the allocation.
> > + * @TYPE: type of structure to allocate space for.
> > + * @FAM: The name of the flexible array member of @TYPE structure.
> > + * @COUNT: how many @FAM elements to allocate space for.
> > + *
> > + * Returns: Newly allocated pointer to @TYPE with @COUNT-many trailing
> > + * @FAM elements, or NULL on failure or if @COUNT cannot be represented
> > + * by the member of @TYPE that counts the @FAM elements (annotated via
> > + * __counted_by()).
> > + */
> > +#define __alloc_flex(KMALLOC, GFP, TYPE, FAM, COUNT)			\
> > +({									\
> > +	const size_t __count = (COUNT);					\
> > +	const size_t __obj_size = struct_size_t(TYPE, FAM, __count);	\
> > +	TYPE *__obj_ptr;						\
> > +	if (WARN_ON_ONCE(overflows_flex_counter_type(TYPE, FAM,	__count))) \
> > +		__obj_ptr = NULL;					\  
...
> Annnd now I typed that I realise that Linus fixed this up in mainline and I was
> working with a stale version of this file :))

I think someone else mentioned it, but having a WARN_ON_ONCE() is there
is really a bad idea.
The code bloat must be stunning.

I won't ask why the #define parameters are all UPPER CASE.

	David



      reply	other threads:[~2026-02-24 11:11 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20251203233029.it.641-kees@kernel.org>
2025-12-03 23:30 ` Kees Cook
2026-01-08 14:06   ` Vlastimil Babka
2026-01-08 17:12     ` Kees Cook
2026-01-08 17:40     ` Kees Cook
2026-01-09 17:12   ` Vlastimil Babka
2026-02-24 10:26   ` Lorenzo Stoakes
2026-02-24 11:11     ` David Laight [this message]

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