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 E6D1AC63797 for ; Sun, 15 Jan 2023 20:46:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231160AbjAOUqR (ORCPT ); Sun, 15 Jan 2023 15:46:17 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59488 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231346AbjAOUqM (ORCPT ); Sun, 15 Jan 2023 15:46:12 -0500 Received: from netrider.rowland.org (netrider.rowland.org [192.131.102.5]) by lindbergh.monkeyblade.net (Postfix) with SMTP id 8ED1D13503 for ; Sun, 15 Jan 2023 12:46:11 -0800 (PST) Received: (qmail 106827 invoked by uid 1000); 15 Jan 2023 15:46:10 -0500 Date: Sun, 15 Jan 2023 15:46:10 -0500 From: Alan Stern To: "Paul E. McKenney" Cc: Jonas Oberhauser , Peter Zijlstra , "parri.andrea" , 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: <20230113200706.GI4028633@paulmck-ThinkPad-P17-Gen-1> <20230113203241.GA2958699@paulmck-ThinkPad-P17-Gen-1> <136d019d8c8049f6b737627df830e66f@huawei.com> <20230114175343.GF2948950@paulmck-ThinkPad-P17-Gen-1> <20230114181537.GA493203@paulmck-ThinkPad-P17-Gen-1> <20230115051510.GG2948950@paulmck-ThinkPad-P17-Gen-1> <20230115181052.GJ2948950@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230115181052.GJ2948950@paulmck-ThinkPad-P17-Gen-1> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Jan 15, 2023 at 10:10:52AM -0800, Paul E. McKenney wrote: > On Sun, Jan 15, 2023 at 11:23:31AM -0500, Alan Stern wrote: > > On Sat, Jan 14, 2023 at 09:15:10PM -0800, Paul E. McKenney wrote: > > > What am I missing here? > > > > I don't think you're missing anything. This is a matter for Boqun or > > Luc; it must have something to do with the way herd treats the > > srcu_read_lock() and srcu_read_unlock() primitives. > > It looks like we need something that tracks (data | rf)* between > the return value of srcu_read_lock() and the second parameter of > srcu_read_unlock(). The reason for rf rather than rfi is the upcoming > srcu_down_read() and srcu_up_read(). Or just make herd treat srcu_read_lock(s) as an annotated equivalent of READ_ONCE(&s) and srcu_read_unlock(s, v) as an annotated equivalent of WRITE_ONCE(s, v). But with some special accomodation to avoid interaction with the new carry-dep relation. > But what I will do in the meantime is to switch back to a commit that > simply flags nesting of same-srcu_struct SRCU read-side critical sections, > while blindly assuming that the return value of a given srcu_read_lock() > is passed in to the corresponding srcu_read_unlock(): > > ------------------------------------------------------------------------ > > (* Compute matching pairs of Srcu-lock and Srcu-unlock, but prohibit nesting *) > let srcu-unmatched = Srcu-lock | Srcu-unlock > let srcu-unmatched-po = ([srcu-unmatched] ; po ; [srcu-unmatched]) & loc > let srcu-unmatched-locks-to-unlock = ([Srcu-lock] ; po ; [Srcu-unlock]) & loc > let srcu-rscs = srcu-unmatched-locks-to-unlock \ (srcu-unmatched-po ; srcu-unmatched-po) > > (* Validate nesting *) > flag ~empty Srcu-lock \ domain(srcu-rscs) as unbalanced-srcu-locking > flag ~empty Srcu-unlock \ range(srcu-rscs) as unbalanced-srcu-locking > > (* 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 > > ------------------------------------------------------------------------ > > Or is there some better intermediate position that could be taken? Do you mean go back to the current linux-kernel.bell? The code you wrote above is different, since it prohibits nesting. Alan