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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9B819C004D4 for ; Thu, 19 Jan 2023 22:22:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229734AbjASWWc (ORCPT ); Thu, 19 Jan 2023 17:22:32 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54452 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230198AbjASWVS (ORCPT ); Thu, 19 Jan 2023 17:21:18 -0500 Received: from netrider.rowland.org (netrider.rowland.org [192.131.102.5]) by lindbergh.monkeyblade.net (Postfix) with SMTP id 1971E45897 for ; Thu, 19 Jan 2023 14:04:50 -0800 (PST) Received: (qmail 10391 invoked by uid 1000); 19 Jan 2023 17:04:49 -0500 Date: Thu, 19 Jan 2023 17:04:49 -0500 From: Alan Stern To: "Paul E. McKenney" Cc: Jonas Oberhauser , Andrea Parri , Jonas Oberhauser , Peter Zijlstra , will , "boqun.feng" , npiggin , dhowells , "j.alglave" , "luc.maranget" , akiyks , dlustig , joel , urezki , quic_neeraju , frederic , Kernel development list Subject: Re: Internal vs. external barriers (was: Re: Interesting LKMM litmus test) Message-ID: References: <3dabbcfb-858c-6aa0-6824-05b8cc8e9cdb@gmail.com> <20230118201918.GI2948950@paulmck-ThinkPad-P17-Gen-1> <20230118211201.GL2948950@paulmck-ThinkPad-P17-Gen-1> <09f084d2-6128-7f83-b2a5-cbe236b1678d@huaweicloud.com> <20230119001147.GN2948950@paulmck-ThinkPad-P17-Gen-1> <0fae983b-2a7c-d44e-8881-53d5cc053f09@huaweicloud.com> <20230119184107.GT2948950@paulmck-ThinkPad-P17-Gen-1> <20230119215304.GA2948950@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230119215304.GA2948950@paulmck-ThinkPad-P17-Gen-1> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 19, 2023 at 01:53:04PM -0800, Paul E. McKenney wrote: > On Thu, Jan 19, 2023 at 02:51:53PM -0500, Alan Stern wrote: > > Index: usb-devel/tools/memory-model/linux-kernel.bell > > =================================================================== > > --- usb-devel.orig/tools/memory-model/linux-kernel.bell > > +++ usb-devel/tools/memory-model/linux-kernel.bell > > @@ -53,38 +53,30 @@ let rcu-rscs = let rec > > in matched > > > > (* Validate nesting *) > > -flag ~empty Rcu-lock \ domain(rcu-rscs) as unbalanced-rcu-locking > > -flag ~empty Rcu-unlock \ range(rcu-rscs) as unbalanced-rcu-locking > > +flag ~empty Rcu-lock \ domain(rcu-rscs) as unbalanced-rcu-lock > > +flag ~empty Rcu-unlock \ range(rcu-rscs) as unbalanced-rcu-unlock > > This renaming makes sense to me. But I'll put it in a separate patch, since it's not related to the main purpose of this change. > > > (* Compute matching pairs of nested Srcu-lock and Srcu-unlock *) > > -let srcu-rscs = let rec > > - unmatched-locks = Srcu-lock \ domain(matched) > > - and unmatched-unlocks = Srcu-unlock \ range(matched) > > - and unmatched = unmatched-locks | unmatched-unlocks > > - and unmatched-po = ([unmatched] ; po ; [unmatched]) & loc > > - and unmatched-locks-to-unlocks = > > - ([unmatched-locks] ; po ; [unmatched-unlocks]) & loc > > - and matched = matched | (unmatched-locks-to-unlocks \ > > - (unmatched-po ; unmatched-po)) > > - in matched > > +let srcu-rscs = ([Srcu-lock] ; (data | rf)+ ; [Srcu-unlock]) & loc > > The point of the "+" instead of the "*" is to avoid LKMM being confused by > an srcu_read_lock() immediately preceding an unrelated srcu_read_unlock(), > right? Or am I missing something more subtle? No, and it's not to avoid confusion. It merely indicates that there has to be at least one instance of data or rf here; we will never have a case where the lock and the unlock are the same event. > > > (* Validate nesting *) > > -flag ~empty Srcu-lock \ domain(srcu-rscs) as unbalanced-srcu-locking > > -flag ~empty Srcu-unlock \ range(srcu-rscs) as unbalanced-srcu-locking > > +flag ~empty Srcu-lock \ domain(srcu-rscs) as unbalanced-srcu-lock > > +flag ~empty Srcu-unlock \ range(srcu-rscs) as unbalanced-srcu-unlock > > +flag ~empty (srcu-rscs^-1 ; srcu-rscs) \ id as multiple-srcu-matches > > > > (* Check for use of synchronize_srcu() inside an RCU critical section *) > > flag ~empty rcu-rscs & (po ; [Sync-srcu] ; po) as invalid-sleep > > > > (* Validate SRCU dynamic match *) > > -flag ~empty different-values(srcu-rscs) as srcu-bad-nesting > > +flag ~empty different-values(srcu-rscs) as bad-srcu-value-match > > > > (* Compute marked and plain memory accesses *) > > let Marked = (~M) | IW | Once | Release | Acquire | domain(rmw) | range(rmw) | > > - LKR | LKW | UL | LF | RL | RU > > + LKR | LKW | UL | LF | RL | RU | Srcu-lock | Srcu-unlock > > let Plain = M \ Marked > > > > (* Redefine dependencies to include those carried through plain accesses *) > > -let carry-dep = (data ; rfi)* > > +let carry-dep = (data ; [~ Srcu-unlock] ; rfi)* > > The "[~ Srcu-unlock]" matches the store that bridges the data and rfi", > correct? Right. > > > let addr = carry-dep ; addr > > let ctrl = carry-dep ; ctrl > > let data = carry-dep ; data > > Index: usb-devel/tools/memory-model/linux-kernel.def > > =================================================================== > > --- usb-devel.orig/tools/memory-model/linux-kernel.def > > +++ usb-devel/tools/memory-model/linux-kernel.def > > @@ -49,8 +49,10 @@ synchronize_rcu() { __fence{sync-rcu}; } > > synchronize_rcu_expedited() { __fence{sync-rcu}; } > > > > // SRCU > > -srcu_read_lock(X) __srcu{srcu-lock}(X) > > -srcu_read_unlock(X,Y) { __srcu{srcu-unlock}(X,Y); } > > +srcu_read_lock(X) __load{srcu-lock}(*X) > > +srcu_read_unlock(X,Y) { __store{srcu-unlock}(*X,Y); } > > +srcu_down_read(X) __load{srcu-lock}(*X) > > +srcu_up_read(X,Y) { __store{srcu-unlock}(*X,Y); } > > And here srcu_down_read() and srcu_up_read() are synonyms for > srcu_read_lock() and srcu_read_unlock(), respectively, which I believe > should suffice. > > > synchronize_srcu(X) { __srcu{sync-srcu}(X); } > > synchronize_srcu_expedited(X) { __srcu{sync-srcu}(X); } > > So this looks quite reasonable to me. Okay, good. In theory we could check for read_lock and read_unlock on different CPUs, but I don't think it's worth the trouble. Alan