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 CA4D6C05027 for ; Fri, 20 Jan 2023 15:32:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231459AbjATPct (ORCPT ); Fri, 20 Jan 2023 10:32:49 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34700 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231472AbjATPcr (ORCPT ); Fri, 20 Jan 2023 10:32:47 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5D56E1725 for ; Fri, 20 Jan 2023 07:32:44 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id EC37861FA9 for ; Fri, 20 Jan 2023 15:32:43 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5703AC433EF; Fri, 20 Jan 2023 15:32:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1674228763; bh=0XaUav4RueNVm96Ywl+Yh8XPQ+ZnAL0snvgSSziw1Sg=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=NS9RhnxdY2+K41whvY7LIUidI3DiDpqXfPnGrG50UuV/jdx0aWqiwFbJVc4ca3lci td/Z6KIMWnUTDGb6b9wmp0qrsFv6wv38oLIOnwl4+GFy/msrfuEtk/ymomDzDsSRHU bScz02TMnpdAjeP7vEayd8oPfTyJ0Uko5u9NiafvfwIV54dyr6a6Km33l78x14p7v7 v/Fc1owt0K9wtZMufJwGPUNY6exa5oNUugs8KlK2ATRY21fIzlGdGt3fzsQF1NgWLO S1blgt9Kop6onqCJ7o8yWQwluA0XoVbEYLfbT268MjiiqbJQI6kqbV7hUK4INsBS1C bmXvlMXfNo3OQ== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id E66635C0DFC; Fri, 20 Jan 2023 07:32:42 -0800 (PST) Date: Fri, 20 Jan 2023 07:32:42 -0800 From: "Paul E. McKenney" To: Jonas Oberhauser Cc: 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: <20230120153242.GE2948950@paulmck-ThinkPad-P17-Gen-1> Reply-To: paulmck@kernel.org References: <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> <126e32b7-caa7-0a1e-4589-885aef7c5a39@huaweicloud.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 20, 2023 at 01:51:01PM +0100, Jonas Oberhauser wrote: > I'm not going to get it right today, am I? Believe me, I know that feeling! Open-source development is therefore an extremely good character-building exercise. At least that is what I keep telling myself. ;-) > +let srcu-rscs = ([Srcu-lock] ; (data ; [~ Srcu-unlock] ; rfe) * ; data ; > [Srcu-unlock]) & loc > > I see now that I copied the format from your message but without realizing > the original had a `|` where I have a `;`. > I hope this version is finally right and perhaps more natural than the (data > | rf) version, considering rf can't actually appear in most places and this > more closely matches carry-dep;data. > But of course feel free to use > +let srcu-rscs = ([Srcu-lock] ; (data  | [~ Srcu-unlock] ; rf)+ ; > [Srcu-unlock]) & loc > instead if you prefer. Ah, herd7 could see an rf link between any srcu_read_unlock() and any "later" srcu_read_lock(), couldn't it? Good catch!!! I took this last one, adding parentheses that might well be unnecessary. (You see, herd7 was complaining about cut-and-paste, possibly due to alternative character sets, so I indulged in a bit of diagnostic-driven development.) let srcu-rscs = ([Srcu-lock] ; (data | ([~ Srcu-unlock] ; rf))+ ; [Srcu-unlock]) & loc The reason for favoring "rf" over "rfe" is the possibility of a litmus test where the process containing the srcu_down_read() sometimes but not always also has the matching srcu_up_read(). Perhaps a pair of "if" statements control which process does the matching srcu_up_read(). With this change, all of the C-srcu-nest-*.litmus tests act as expected. And thank you!!! Thanx, Paul > have fun, jonas > > > On 1/20/2023 1:34 PM, Jonas Oberhauser wrote: > > I just realized I made a mistake in my earlier response to this message; > > you still need the rf for passing the cookie across threads. > > Perhaps it's better to just also exclude srcu_unlock type events > > explicitly here. > > > > +let srcu-rscs = ([Srcu-lock] ; (data ; [~ Srcu-unlock] ; rf) + ; > > [Srcu-unlock]) & loc > > > > > > best wishes, > > jonas > > > > On 1/20/2023 4:55 AM, Paul E. McKenney wrote: > > > On Thu, Jan 19, 2023 at 02:51:53PM -0500, Alan Stern wrote: > > > > On Thu, Jan 19, 2023 at 10:41:07AM -0800, Paul E. McKenney wrote: > > > > > In contrast, this actually needs srcu_down_read() and srcu_up_read(): > > > > > > > > > > ------------------------------------------------------------------------ > > > > > > > > > > > > > > > C C-srcu-nest-6 > > > > > > > > > > (* > > > > >   * Result: Never > > > > >   * > > > > >   * Flag unbalanced-srcu-locking > > > > >   * This would be valid for srcu_down_read() and srcu_up_read(). > > > > >   *) > > > > > > > > > > {} > > > > > > > > > > P0(int *x, int *y, struct srcu_struct *s1, int *idx) > > > > > { > > > > >     int r2; > > > > >     int r3; > > > > > > > > > >     r3 = srcu_down_read(s1); > > > > >     WRITE_ONCE(*idx, r3); > > > > >     r2 = READ_ONCE(*y); > > > > > } > > > > > > > > > > P1(int *x, int *y, struct srcu_struct *s1, int *idx) > > > > > { > > > > >     int r1; > > > > >     int r3; > > > > > > > > > >     r1 = READ_ONCE(*x); > > > > >     r3 = READ_ONCE(*idx); > > > > >     srcu_up_read(s1, r3); > > > > > } > > > > > > > > > > P2(int *x, int *y, struct srcu_struct *s1) > > > > > { > > > > >     WRITE_ONCE(*y, 1); > > > > >     synchronize_srcu(s1); > > > > >     WRITE_ONCE(*x, 1); > > > > > } > > > > > > > > > > locations [0:r1] > > > > > exists (1:r1=1 /\ 0:r2=0) > > > > I modified this litmus test by adding a flag variable with an > > > > smp_store_release in P0, an smp_load_acquire in P1, and a filter clause > > > > to ensure that P1 reads the flag and idx from P1. > > > > > > > > With the patch below, the results were as expected: > > > > > > > > Test C-srcu-nest-6 Allowed > > > > States 3 > > > > 0:r1=0; 0:r2=0; 1:r1=0; > > > > 0:r1=0; 0:r2=1; 1:r1=0; > > > > 0:r1=0; 0:r2=1; 1:r1=1; > > > > No > > > > Witnesses > > > > Positive: 0 Negative: 3 > > > > Condition exists (1:r1=1 /\ 0:r2=0) > > > > Observation C-srcu-nest-6 Never 0 3 > > > > Time C-srcu-nest-6 0.04 > > > > Hash=2b010cf3446879fb84752a6016ff88c5 > > > > > > > > It turns out that the idea of removing rf edges from Srcu-unlock events > > > > doesn't work well.  The missing edges mess up herd's calculation of the > > > > fr relation and the coherence axiom.  So I've gone back to filtering > > > > those edges out of carry-dep. > > > > > > > > Also, Boqun's suggestion for flagging ordinary accesses to SRCU > > > > structures no longer works, because the lock and unlock operations now > > > > _are_ normal accesses.  I removed that check too, but it shouldn't hurt > > > > much because I don't expect to encounter litmus tests that try to read > > > > or write srcu_structs directly. > > > > > > > > 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 +53,30 @@ 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 > > > >     (* 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 > > > >     (* 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); } > > > 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.) > > > > > > 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!!! > > > > > > I also started a regression test, hopefully without pilot error.  :-/ > > > > > >                             Thanx, Paul > > >