From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 3AF3EC4345F for ; Fri, 3 May 2024 10:36:32 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 9DFF910FADD; Fri, 3 May 2024 10:36:31 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=fail reason="signature verification failed" (2048-bit key; secure) header.d=infradead.org header.i=@infradead.org header.b="N8I4+Cwi"; dkim-atps=neutral Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) by gabe.freedesktop.org (Postfix) with ESMTPS id 8E18610FA90; Fri, 3 May 2024 10:36:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=qh5Wc3QqXgam82TMaOdVdy+cfP6ZNoEKs7ddCVe4jPY=; b=N8I4+CwiBUkzZYIyGzOqQsvzoP cCulMNJhaL2ygzPgYmNxiIytFGF+IHAZTJlW+4byTl+H1wU91wfyhXytPSpMyruKM0qH5KSX0/zb3 M0q8Xbygslb8bYQIpKyIjcsZNaQg/QlWYyn52lYXcksuWoDoJPjWtlzs918/ctl5xS4pp+70AejpZ OhT/9b+OOu90NRC9JXP0qfZxYlcy+pcNpDPFbgfrnHw1FTRS23pxj0DUFeYKUk3VnYsJropW0Di81 TbrsNflYBNuzXjCwiY53z3m6L9fTjcAMDy3NRSeShDj/z2uaw7qLx2j5fikTkkfH5hfv1oFxw5CPT fv3XU5Zg==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.97.1 #2 (Red Hat Linux)) id 1s2qH0-00000000W9c-2SYt; Fri, 03 May 2024 10:36:14 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 402B93001FD; Fri, 3 May 2024 12:36:14 +0200 (CEST) Date: Fri, 3 May 2024 12:36:14 +0200 From: Peter Zijlstra To: Christian Brauner Cc: Kees Cook , Al Viro , Jan Kara , linux-fsdevel@vger.kernel.org, Zack Rusin , Broadcom internal kernel review list , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Daniel Vetter , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , Andi Shyti , Lucas De Marchi , Matt Atwood , Matthew Auld , Nirmoy Das , Jonathan Cavitt , Will Deacon , Boqun Feng , Mark Rutland , Kent Overstreet , Masahiro Yamada , Nathan Chancellor , Nicolas Schier , Andrew Morton , 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 Message-ID: <20240503103614.GF30852@noisy.programming.kicks-ass.net> References: <20240502223341.1835070-5-keescook@chromium.org> <20240502224250.GM2118490@ZenIV> <202405021548.040579B1C@keescook> <20240502231228.GN2118490@ZenIV> <202405021620.C8115568@keescook> <20240502234152.GP2118490@ZenIV> <202405021708.267B02842@keescook> <20240503001445.GR2118490@ZenIV> <202405021736.574A688@keescook> <20240503-inventar-braut-c82e15e56a32@brauner> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240503-inventar-braut-c82e15e56a32@brauner> X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" 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?