From: Peter Zijlstra <peterz@infradead.org>
To: Christian Brauner <brauner@kernel.org>
Cc: Kees Cook <keescook@chromium.org>,
Al Viro <viro@zeniv.linux.org.uk>, Jan Kara <jack@suse.cz>,
linux-fsdevel@vger.kernel.org,
Zack Rusin <zack.rusin@broadcom.com>,
Broadcom internal kernel review list
<bcm-kernel-feedback-list@broadcom.com>,
Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
Maxime Ripard <mripard@kernel.org>,
Thomas Zimmermann <tzimmermann@suse.de>,
David Airlie <airlied@gmail.com>, Daniel Vetter <daniel@ffwll.ch>,
Jani Nikula <jani.nikula@linux.intel.com>,
Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
Rodrigo Vivi <rodrigo.vivi@intel.com>,
Tvrtko Ursulin <tursulin@ursulin.net>,
Andi Shyti <andi.shyti@linux.intel.com>,
Lucas De Marchi <lucas.demarchi@intel.com>,
Matt Atwood <matthew.s.atwood@intel.com>,
Matthew Auld <matthew.auld@intel.com>,
Nirmoy Das <nirmoy.das@intel.com>,
Jonathan Cavitt <jonathan.cavitt@intel.com>,
Will Deacon <will@kernel.org>, Boqun Feng <boqun.feng@gmail.com>,
Mark Rutland <mark.rutland@arm.com>,
Kent Overstreet <kent.overstreet@linux.dev>,
Masahiro Yamada <masahiroy@kernel.org>,
Nathan Chancellor <nathan@kernel.org>,
Nicolas Schier <nicolas@fjasle.eu>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
intel-gfx@lists.freedesktop.org, linux-kbuild@vger.kernel.org,
linux-hardening@vger.kernel.org
Subject: Re: [PATCH 5/5] fs: Convert struct file::f_count to refcount_long_t
Date: Fri, 3 May 2024 12:36:14 +0200 [thread overview]
Message-ID: <20240503103614.GF30852@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <20240503-inventar-braut-c82e15e56a32@brauner>
On Fri, May 03, 2024 at 11:37:25AM +0200, Christian Brauner wrote:
> On Thu, May 02, 2024 at 05:41:23PM -0700, Kees Cook wrote:
> > On Fri, May 03, 2024 at 01:14:45AM +0100, Al Viro wrote:
> > > On Thu, May 02, 2024 at 05:10:18PM -0700, Kees Cook wrote:
> > >
> > > > But anyway, there needs to be a general "oops I hit 0"-aware form of
> > > > get_file(), and it seems like it should just be get_file() itself...
> > >
> > > ... which brings back the question of what's the sane damage mitigation
> > > for that. Adding arseloads of never-exercised failure exits is generally
> > > a bad idea - it's asking for bitrot and making the thing harder to review
> > > in future.
> >
> > Linus seems to prefer best-effort error recovery to sprinkling BUG()s
> > around. But if that's really the solution, then how about get_file()
> > switching to to use inc_not_zero and BUG on 0?
>
> Making get_file() return an error is not an option. For all current
> callers that's pointless churn for a condition that's not supposed to
> happen at all.
>
> Additionally, iirc *_inc_not_zero() variants are implemented with
> try_cmpxchg() which scales poorly under contention for a condition
> that's not supposed to happen.
unsigned long old = atomic_long_fetch_inc_relaxed(&f->f_count);
WARN_ON(!old);
Or somesuch might be an option?
next prev parent reply other threads:[~2024-05-03 10:36 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-02 22:33 [PATCH 0/5] fs: Do not allow get_file() to resurrect 0 f_count Kees Cook
2024-05-02 22:33 ` [PATCH 1/5] " Kees Cook
2024-05-02 22:53 ` Jann Horn
2024-05-02 23:03 ` Kees Cook
2024-05-03 9:02 ` Christian Brauner
2024-05-06 10:41 ` Hillf Danton
2024-05-02 22:33 ` [PATCH 2/5] drm/vmwgfx: Do not directly manipulate file->f_count Kees Cook
2024-05-02 22:33 ` [PATCH 3/5] drm/i915: " Kees Cook
2024-05-02 22:33 ` [PATCH 4/5] refcount: Introduce refcount_long_t and APIs Kees Cook
2024-05-06 8:04 ` kernel test robot
2024-05-02 22:33 ` [PATCH 5/5] fs: Convert struct file::f_count to refcount_long_t Kees Cook
2024-05-02 22:42 ` Al Viro
2024-05-02 22:52 ` Kees Cook
2024-05-02 23:12 ` Al Viro
2024-05-02 23:21 ` Kees Cook
2024-05-02 23:41 ` Al Viro
2024-05-03 0:10 ` Kees Cook
2024-05-03 0:14 ` Al Viro
2024-05-03 0:41 ` Kees Cook
2024-05-03 9:37 ` Christian Brauner
2024-05-03 10:36 ` Peter Zijlstra [this message]
2024-05-03 11:35 ` Christian Brauner
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