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 CCE91C7EE23 for ; Fri, 26 May 2023 16:42:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230046AbjEZQmE (ORCPT ); Fri, 26 May 2023 12:42:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43836 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229664AbjEZQmD (ORCPT ); Fri, 26 May 2023 12:42:03 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EB777BC; Fri, 26 May 2023 09:42:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=/2QSTLGqD4iT4FdYiOFZiER0pBrlULh2+1/cvz6IreM=; b=iTZt2k9etvAGrB42jErQZIlq9M rBI0aflYiIqy6tAsDZmmQONBFt8owIQj+EIovr1U68zHfLJWg1VrxkF5ud1yg1dXpE+bgWe/9knP0 R7S9hvAFuqWq11R2s9yd/py4UTJYMl4g1rRo/n1cb135zW2DuOqQsDEZRN5z9ONPzHa8tX60LUQSh y3u0OMhufNpUGUq0Roxm0wvXWCBnGjzB8mal1/TEYXDaO0OMBJy48jdp1j9o7LYneEogdV7lo5tAz 5+zG4as0eaiocVGvPyeyoE9M6ZUrbvoxqjUaT7e0M7WvWrGxp3xk72+zzfs5WxpB05CGd5+wX4NI5 M9qSiJSA==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1q2aVS-002xkV-23; Fri, 26 May 2023 16:41:34 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 55ECB3002F0; Fri, 26 May 2023 18:41:31 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 103F522163BD2; Fri, 26 May 2023 18:41:31 +0200 (CEST) Date: Fri, 26 May 2023 18:41:30 +0200 From: Peter Zijlstra To: Greg KH Cc: torvalds@linux-foundation.org, keescook@chromium.org, pbonzini@redhat.com, linux-kernel@vger.kernel.org, ojeda@kernel.org, ndesaulniers@google.com, mingo@redhat.com, will@kernel.org, longman@redhat.com, boqun.feng@gmail.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, paulmck@kernel.org, frederic@kernel.org, quic_neeraju@quicinc.com, joel@joelfernandes.org, josh@joshtriplett.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, qiang1.zhang@intel.com, rcu@vger.kernel.org, tj@kernel.org, tglx@linutronix.de Subject: Re: [RFC][PATCH 2/2] sched: Use fancy new guards Message-ID: <20230526164130.GA4053578@hirez.programming.kicks-ass.net> References: <20230526150549.250372621@infradead.org> <20230526151947.027972233@infradead.org> <2023052626-blunderer-delegator-4b82@gregkh> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2023052626-blunderer-delegator-4b82@gregkh> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 26, 2023 at 05:25:58PM +0100, Greg KH wrote: > On Fri, May 26, 2023 at 05:05:51PM +0200, Peter Zijlstra wrote: > > Convert kernel/sched/core.c to use the fancy new guards to simplify > > the error paths. > > That's slightly crazy... > > I like the idea, but is this really correct: > > > > > > Signed-off-by: Peter Zijlstra (Intel) > > --- > > kernel/sched/core.c | 1223 +++++++++++++++++++++++---------------------------- > > kernel/sched/sched.h | 39 + > > 2 files changed, 595 insertions(+), 667 deletions(-) > > > > --- a/kernel/sched/core.c > > +++ b/kernel/sched/core.c > > @@ -1097,24 +1097,21 @@ int get_nohz_timer_target(void) > > > > hk_mask = housekeeping_cpumask(HK_TYPE_TIMER); > > > > - rcu_read_lock(); > > - for_each_domain(cpu, sd) { > > - for_each_cpu_and(i, sched_domain_span(sd), hk_mask) { > > - if (cpu == i) > > - continue; > > + void_scope(rcu) { > > + for_each_domain(cpu, sd) { > > + for_each_cpu_and(i, sched_domain_span(sd), hk_mask) { > > + if (cpu == i) > > + continue; > > > > - if (!idle_cpu(i)) { > > - cpu = i; > > - goto unlock; > > + if (!idle_cpu(i)) > > + return i; > > You can call return from within a "scope" and it will clean up properly? Yep, that's the main feature here. > I tried to read the cpp "mess" but couldn't figure out how to validate > this at all, have a set of tests for this somewhere? I have it in userspace with printf, but yeah, I'll go make a selftest somewhere. One advantage of using the scheduler locks as testbed is that if you get it wrong it burns *real* fast -- been there done that etc. > Anyway, the naming is whack, but I don't have a proposed better name, > except you might want to put "scope_" as the prefix not the suffix, but > then that might look odd to, so who knows. Yeah, naming is certainly crazy, but I figured I should get it all working before spending too much time on that. I can certainly do 's/lock_scope/scope_lock/g' on it all. > But again, the idea is good, it might save us lots of "you forgot to > clean this up on the error path" mess that we are getting constant churn > for these days... That's the goal...