linux-hardening - Re: [PATCH 0/3] enumarated refcounts, for debugging refcount issues

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Message-ID: <yd3f6ie56x2dbagqycwluxtz7inrmbub5fg7omp226vrdvxtb2@sjn23uj3r6t7>
Date: Sun, 20 Apr 2025 21:27:26 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Kees Cook <kees@...nel.org>
Cc: linux-bcachefs@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] enumarated refcounts, for debugging refcount issues

On Sun, Apr 20, 2025 at 06:08:41PM -0700, Kees Cook wrote:
> On Sun, Apr 20, 2025 at 11:59:13AM -0400, Kent Overstreet wrote:
> > Not sure we have a list for library code, but this might be of interest
> > to anyone who's had to debug refcount issues on refs with lots of users
> > (filesystem people), and I know the hardening folks deal with refcounts
> > a lot.
> 
> Why not use refcount_t instead of atomic_t?

It's rather pointless here since percpu refcounts don't (and can't)
support saturation, and atomic_long_t should always suffice - you'd have
to be doing something particularly bizarre for it not to, since
refcounts generally count things in memory.

Out of curiousity, has overflow of an atomic_long_t refcount ever been
observed?