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 X-Spam-Level: X-Spam-Status: No, score=-11.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D631AC43461 for ; Thu, 3 Sep 2020 23:30:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A215A2078E for ; Thu, 3 Sep 2020 23:30:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1599175839; bh=B3pK5zZnU9RKRCpV09z0d2GVM5xHL2b8XThKQbrNalY=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=2WFmvW1IOa9u9RVQkz9W+52xy0y/ydzbSZ46/X5j+Bcuws5jVoiGKPfHjmua2/XJA CmLRSqYNwj2usZpdfIERMx7I5XcjeMgohJijz0/Jtp9AUjAb3mH5hWet8TMb6gwWU1 xSYa0PF0JNbQcbIVAFPglh5m48YXJYZraKWZdoB8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729547AbgICXai (ORCPT ); Thu, 3 Sep 2020 19:30:38 -0400 Received: from mail.kernel.org ([198.145.29.99]:55164 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728271AbgICXai (ORCPT ); Thu, 3 Sep 2020 19:30:38 -0400 Received: from paulmck-ThinkPad-P72.home (unknown [50.45.173.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 67CE320786; Thu, 3 Sep 2020 23:30:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1599175837; bh=B3pK5zZnU9RKRCpV09z0d2GVM5xHL2b8XThKQbrNalY=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=LwWR5naI1s2ii2yNOtdTNaSVrP09eFKVIfqFTWOKhQuPyIOKvXAgGiY0Ubs+r27mO SZhjVj/WmadlsOw71vF7bLirPmJzrVf0TrtBc7UlojTNUeVrFAwpo6HlgQdZ8ZlQae 4xcAN0CxGkJcgpEMws82bhehpK2iUXgyflAufPQo= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 4C62A3522636; Thu, 3 Sep 2020 16:30:37 -0700 (PDT) Date: Thu, 3 Sep 2020 16:30:37 -0700 From: "Paul E. McKenney" To: Boqun Feng Cc: peterz@infradead.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, stern@rowland.harvard.edu, parri.andrea@gmail.com, will@kernel.org, npiggin@gmail.com, dhowells@redhat.com, j.alglave@ucl.ac.uk, luc.maranget@inria.fr, akiyks@gmail.com Subject: Re: [PATCH kcsan 6/9] tools/memory-model: Expand the cheatsheet.txt notion of relaxed Message-ID: <20200903233037.GW29330@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200831182012.GA1965@paulmck-ThinkPad-P72> <20200831182037.2034-6-paulmck@kernel.org> <20200902035448.GC49492@debian-boqun.qqnc3lrjykvubdpftowmye0fmh.lx.internal.cloudapp.net> <20200902101412.GC1362448@hirez.programming.kicks-ass.net> <20200902123715.GD49492@debian-boqun.qqnc3lrjykvubdpftowmye0fmh.lx.internal.cloudapp.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200902123715.GD49492@debian-boqun.qqnc3lrjykvubdpftowmye0fmh.lx.internal.cloudapp.net> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 02, 2020 at 08:37:15PM +0800, Boqun Feng wrote: > On Wed, Sep 02, 2020 at 12:14:12PM +0200, peterz@infradead.org wrote: > > On Wed, Sep 02, 2020 at 11:54:48AM +0800, Boqun Feng wrote: > > > On Mon, Aug 31, 2020 at 11:20:34AM -0700, paulmck@kernel.org wrote: > > > > From: "Paul E. McKenney" > > > > > > > > This commit adds a key entry enumerating the various types of relaxed > > > > operations. > > > > > > > > Signed-off-by: Paul E. McKenney > > > > --- > > > > tools/memory-model/Documentation/cheatsheet.txt | 27 ++++++++++++++----------- > > > > 1 file changed, 15 insertions(+), 12 deletions(-) > > > > > > > > diff --git a/tools/memory-model/Documentation/cheatsheet.txt b/tools/memory-model/Documentation/cheatsheet.txt > > > > index 33ba98d..31b814d 100644 > > > > --- a/tools/memory-model/Documentation/cheatsheet.txt > > > > +++ b/tools/memory-model/Documentation/cheatsheet.txt > > > > @@ -5,7 +5,7 @@ > > > > > > > > Store, e.g., WRITE_ONCE() Y Y > > > > Load, e.g., READ_ONCE() Y Y Y Y > > > > -Unsuccessful RMW operation Y Y Y Y > > > > +Relaxed operation Y Y Y Y > > > > rcu_dereference() Y Y Y Y > > > > Successful *_acquire() R Y Y Y Y Y Y > > > > Successful *_release() C Y Y Y W Y > > > > @@ -17,14 +17,17 @@ smp_mb__before_atomic() CP Y Y Y a a a a Y > > > > smp_mb__after_atomic() CP a a Y Y Y Y Y Y > > > > > > > > > > > > -Key: C: Ordering is cumulative > > > > - P: Ordering propagates > > > > - R: Read, for example, READ_ONCE(), or read portion of RMW > > > > - W: Write, for example, WRITE_ONCE(), or write portion of RMW > > > > - Y: Provides ordering > > > > - a: Provides ordering given intervening RMW atomic operation > > > > - DR: Dependent read (address dependency) > > > > - DW: Dependent write (address, data, or control dependency) > > > > - RMW: Atomic read-modify-write operation > > > > - SELF: Orders self, as opposed to accesses before and/or after > > > > - SV: Orders later accesses to the same variable > > > > +Key: Relaxed: A relaxed operation is either a *_relaxed() RMW > > > > + operation, an unsuccessful RMW operation, or one of > > > > + the atomic_read() and atomic_set() family of operations. > > > > > > To be accurate, atomic_set() doesn't return any value, so it cannot be > > > ordered against DR and DW ;-) > > > > Surely DW is valid for any store. > > > > IIUC, the DW colomn stands for whether the corresponding operation (in > this case, it's atomic_set()) is ordered any write that depends on this > operation. I don't think there is a write->write dependency, so DW for > atomic_set() should not be Y, just as the DW for WRITE_ONCE(). > > > > I think we can split the Relaxed family into two groups: > > > > > > void Relaxed: atomic_set() or atomic RMW operations that don't return > > > any value (e.g atomic_inc()) > > > > > > non-void Relaxed: a *_relaxed() RMW operation, an unsuccessful RMW > > > operation, or atomic_read(). > > > > > > And "void Relaxed" is similar to WRITE_ONCE(), only has "Self" and "SV" > > > equal "Y", while "non-void Relaxed" plays the same rule as "Relaxed" > > > in this patch. > > > > > > Thoughts? > > > > I get confused by the mention of all this atomic_read() atomic_set() > > crud in the first place, why are they called out specifically from any > > other regular load/store ? > > Agreed. Probably we should fold those two operations into "Load" and > "Store" cases. All good points. How about like this, adding "Relaxed" to the WRITE_ONCE() and READ_ONCE() rows and "RMW" to the "Relaxed operation" row? The file contents are followed by a diff against the previous version. Thanx, Paul ------------------------------------------------------------------------ Prior Operation Subsequent Operation --------------- --------------------------- C Self R W RMW Self R W DR DW RMW SV -- ---- - - --- ---- - - -- -- --- -- Relaxed store Y Y Relaxed load Y Y Y Y Relaxed RMW operation Y Y Y Y rcu_dereference() Y Y Y Y Successful *_acquire() R Y Y Y Y Y Y Successful *_release() C Y Y Y W Y smp_rmb() Y R Y Y R smp_wmb() Y W Y Y W smp_mb() & synchronize_rcu() CP Y Y Y Y Y Y Y Y Successful full non-void RMW CP Y Y Y Y Y Y Y Y Y Y Y smp_mb__before_atomic() CP Y Y Y a a a a Y smp_mb__after_atomic() CP a a Y Y Y Y Y Y Key: Relaxed: A relaxed operation is either a *_relaxed() RMW operation, an unsuccessful RMW operation, READ_ONCE(), WRITE_ONCE(), or one of the atomic_read() and atomic_set() family of operations. C: Ordering is cumulative P: Ordering propagates R: Read, for example, READ_ONCE(), or read portion of RMW W: Write, for example, WRITE_ONCE(), or write portion of RMW Y: Provides ordering a: Provides ordering given intervening RMW atomic operation DR: Dependent read (address dependency) DW: Dependent write (address, data, or control dependency) RMW: Atomic read-modify-write operation SELF: Orders self, as opposed to accesses before and/or after SV: Orders later accesses to the same variable ------------------------------------------------------------------------ diff --git a/tools/memory-model/Documentation/cheatsheet.txt b/tools/memory-model/Documentation/cheatsheet.txt index 31b814d..4146b8d 100644 --- a/tools/memory-model/Documentation/cheatsheet.txt +++ b/tools/memory-model/Documentation/cheatsheet.txt @@ -3,9 +3,9 @@ C Self R W RMW Self R W DR DW RMW SV -- ---- - - --- ---- - - -- -- --- -- -Store, e.g., WRITE_ONCE() Y Y -Load, e.g., READ_ONCE() Y Y Y Y -Relaxed operation Y Y Y Y +Relaxed store Y Y +Relaxed load Y Y Y Y +Relaxed RMW operation Y Y Y Y rcu_dereference() Y Y Y Y Successful *_acquire() R Y Y Y Y Y Y Successful *_release() C Y Y Y W Y @@ -18,8 +18,9 @@ smp_mb__after_atomic() CP a a Y Y Y Y Y Y Key: Relaxed: A relaxed operation is either a *_relaxed() RMW - operation, an unsuccessful RMW operation, or one of - the atomic_read() and atomic_set() family of operations. + operation, an unsuccessful RMW operation, READ_ONCE(), + WRITE_ONCE(), or one of the atomic_read() and + atomic_set() family of operations. C: Ordering is cumulative P: Ordering propagates R: Read, for example, READ_ONCE(), or read portion of RMW