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 5A8F2C25B4E for ; Fri, 20 Jan 2023 16:14:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229667AbjATQOK (ORCPT ); Fri, 20 Jan 2023 11:14:10 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47644 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229494AbjATQOI (ORCPT ); Fri, 20 Jan 2023 11:14:08 -0500 Received: from netrider.rowland.org (netrider.rowland.org [192.131.102.5]) by lindbergh.monkeyblade.net (Postfix) with SMTP id 698C779EAB for ; Fri, 20 Jan 2023 08:14:07 -0800 (PST) Received: (qmail 38015 invoked by uid 1000); 20 Jan 2023 11:14:06 -0500 Date: Fri, 20 Jan 2023 11:14:06 -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> <20230120035521.GA319650@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230120035521.GA319650@paulmck-ThinkPad-P17-Gen-1> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 19, 2023 at 07:55:21PM -0800, Paul E. McKenney wrote: > And for some initial tests: > > https://github.com/paulmckrcu/litmus/blob/master/manual/kernel/C-srcu-nest-1.litmus > > "Flag multiple-srcu-matches" but otherwise OK. > As a "hail Mary" exercise, I used r4 for the second SRCU > read-side critical section, but this had no effect. > (This flag is expected and seen for #4 below.) Jonas is right about the reason for this. Also, his suggestion for fixing the check in lock.cat makes sense. My revised patch is below. > https://github.com/paulmckrcu/litmus/blob/master/manual/kernel/C-srcu-nest-2.litmus > https://github.com/paulmckrcu/litmus/blob/master/manual/kernel/C-srcu-nest-3.litmus > https://github.com/paulmckrcu/litmus/blob/master/manual/kernel/C-srcu-nest-4.litmus > https://github.com/paulmckrcu/litmus/blob/master/manual/kernel/C-srcu-nest-5.litmus > > All as expected. > > https://github.com/paulmckrcu/litmus/blob/master/manual/kernel/C-srcu-nest-6.litmus > > Get "Flag unbalanced-srcu-lock" and "Flag unbalanced-srcu-unlock", > but this is srcu_down_read() and srcu_up_read(), where this should > be OK. Ah, but I need to do the release/acquire/filter trick. Once > I did that, it works as expected. > > https://github.com/paulmckrcu/litmus/blob/master/manual/kernel/C-srcu-nest-7.litmus > https://github.com/paulmckrcu/litmus/blob/master/manual/kernel/C-srcu-nest-8.litmus > > Both as expected. > > Getting there!!! Good news. Alan 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 +53,31 @@ 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 (* 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 carry-srcu-data = (data ; [~ Srcu-unlock] ; rf)* +let srcu-rscs = ([Srcu-lock] ; carry-srcu-data ; data ; [Srcu-unlock]) & loc (* 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)* 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); } synchronize_srcu(X) { __srcu{sync-srcu}(X); } synchronize_srcu_expedited(X) { __srcu{sync-srcu}(X); } Index: usb-devel/tools/memory-model/lock.cat =================================================================== --- usb-devel.orig/tools/memory-model/lock.cat +++ usb-devel/tools/memory-model/lock.cat @@ -36,9 +36,9 @@ let RU = try RU with emptyset (* Treat RL as a kind of LF: a read with no ordering properties *) let LF = LF | RL -(* There should be no ordinary R or W accesses to spinlocks *) -let ALL-LOCKS = LKR | LKW | UL | LF | RU -flag ~empty [M \ IW] ; loc ; [ALL-LOCKS] as mixed-lock-accesses +(* There should be no ordinary R or W accesses to spinlocks or SRCU structs *) +let ALL-LOCKS = LKR | LKW | UL | LF | RU | Srcu-lock | Srcu-unlock | Sync-srcu +flag ~empty [M \ IW \ ALL-LOCKS] ; loc ; [ALL-LOCKS] as mixed-lock-accesses (* Link Lock-Reads to their RMW-partner Lock-Writes *) let lk-rmw = ([LKR] ; po-loc ; [LKW]) \ (po ; po)