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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 35F34C4332F for ; Wed, 12 Jan 2022 11:06:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1352751AbiALLGc (ORCPT ); Wed, 12 Jan 2022 06:06:32 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57330 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1352738AbiALLGa (ORCPT ); Wed, 12 Jan 2022 06:06:30 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 97823C06173F; Wed, 12 Jan 2022 03:06:29 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; 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=nv9oEebndkSiqv8pTcj7NImvDdA6KxSCBwjzUgND6Ac=; b=taEKJ6bDdHze7bETZnYl9/7wDa i1PB5dTa9T6SL6KmLnXcEdUBEYRvwYZrthrA3g0T1QrqulikClYv9M9HvbNDcUVJb2H7n7NdLliLW IjvOI145W5idiyDI878zCLuASw1nGZxjQgo3mBCuEYVAOyyT3v4NjAfBpVvre+S50zbLfIN+ncqLF EdYH9w6eiC1i03M8nm/At/P5M5zsSY6mqDCtZhyXCJ6G8EtJh7hiXfnaujw8dwc5bThZeAgfc8RhL bl2P43CB+lVqBXcekr+4SfEOyavXzuvyo6bi97AI529TiCHN3jeX+vfa5JU/RHAEW/P2OWsK8Zi94 z5mbKIDA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1n7bSA-0042n8-MV; Wed, 12 Jan 2022 11:06:07 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 4C2FB3001CD; Wed, 12 Jan 2022 12:06:04 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 2C9542B33EC0E; Wed, 12 Jan 2022 12:06:04 +0100 (CET) Date: Wed, 12 Jan 2022 12:06:04 +0100 From: Peter Zijlstra To: Linus Torvalds Cc: Eric Biggers , Suren Baghdasaryan , Johannes Weiner , Tejun Heo , Zefan Li , Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Jonathan Corbet , "open list:DOCUMENTATION" , Linux Kernel Mailing List , Cgroups , stable , Android Kernel Team , syzbot Subject: Re: [PATCH v2 1/1] psi: Fix uaf issue when psi trigger is destroyed while being polled Message-ID: References: <20220111071212.1210124-1-surenb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 11, 2022 at 11:11:32AM -0800, Linus Torvalds wrote: > Of course, in practice, for pointers, the whole "dereference off a > pointer" on the read side *does* imply a barrier in all relevant > situations. So yes, a smp_store_release() -> READ_ONCE() does work in > practice, although it's technically wrong (in particular, it's wrong > on alpha, because of the completely broken memory ordering that alpha > has that doesn't even honor data dependencies as read-side orderings) On a tangent, that actually works, even on Alpha, see commit d646285885154 ("alpha: Override READ_ONCE() with barriered implementation").