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Date: Sat, 22 Nov 2025 14:16:14 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Kees Cook <kees@kernel.org>
Cc: Bill Wendling <morbo@google.com>, linux-kernel@vger.kernel.org,
 "Gustavo A. R. Silva" <gustavoars@kernel.org>, Nathan Chancellor
 <nathan@kernel.org>, Nick Desaulniers <nick.desaulniers+lkml@gmail.com>,
 Justin Stitt <justinstitt@google.com>, Miguel Ojeda <ojeda@kernel.org>,
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 <masahiroy@kernel.org>, Mike Rapoport <rppt@kernel.org>,
 linux-mm@kvack.org, linux-hardening@vger.kernel.org, llvm@lists.linux.dev
Subject: Re: [PATCH 2/2] memblock: annotate struct memblock_type with
 __counted_by_ptr
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On Fri, 21 Nov 2025 16:30:43 -0800 Kees Cook <kees@kernel.org> wrote:

> On Fri, Nov 21, 2025 at 07:39:44PM +0000, Bill Wendling wrote:
> > Add the '__counted_by_ptr' attribute to the 'regions' field of 'struct
> > memblock_type'. The 'regions' field is an array of 'struct
> > memblock_region' and its size is tracked by the 'max' field, which
> > represents the total number of allocated regions.
> 
> As part of any counted_by annotation patch, there needs to be discussion
> in the commit log about how it's been shown to be a safe annotation
> to make. e.g. in this case, if all allocations of "regions" have a
> corresponding "max" assignment, etc. If just "git grep" can't find them
> all, using something like Coccinelle or CodeQL to search for struct
> memblock_type::regions assignments can work.

How is anyone to know these things?  I can't find anything about this
in include/ or Documentation/ or in the relevant commits.

There should be a comment at the __counted_by() definition site, please.

And possibly write a Documentation/ file then change checkpatch to
direct people to that file if they add a counted_by?