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 X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 34715C433E0 for ; Tue, 11 Aug 2020 06:27:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0C3602076B for ; Tue, 11 Aug 2020 06:27:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="WH6Zpbi2" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728081AbgHKG1m (ORCPT ); Tue, 11 Aug 2020 02:27:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33230 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726154AbgHKG1l (ORCPT ); Tue, 11 Aug 2020 02:27:41 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AFDE2C06174A for ; Mon, 10 Aug 2020 23:27:41 -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=tHm64C/K319CawL1Utw9/ujWZDpftWfDesnIuDRE+5s=; b=WH6Zpbi2msSZ0uT5t9XaZ8WIr9 j1QCkVRYlP8mX6dTCAAKSAG+FmMrHkmhMwuOYG/g11ibR9ur1RQeR6wPBhfPuCcRVt8a+ZBR5xd3s JkYrCpnA7AgXL6aDIiG62FkF4OQx6NwN/rfH0rnx6fm2rmJnlTskabmtkRuof2hBaHR40FRKsUWIz vpVZ2LfJX8Qa5UHXQnsUo7LHx+CX/1UXNswg5GhV/QEgx8mLyIP4vfQXUyosKD1U47PRNhM04CV/2 ELKCcrYDUVqmHHT8SPQQuIqhbY6AT1xnwAGpVdGSt89Hxvjld7cZD97oTWnRYi8qyLbZMIxJPpPVD xk67ClZA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=worktop.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1k5Nl0-0001zc-UW; Tue, 11 Aug 2020 06:27:35 +0000 Received: by worktop.programming.kicks-ass.net (Postfix, from userid 1000) id D253A980CA0; Tue, 11 Aug 2020 08:27:33 +0200 (CEST) Date: Tue, 11 Aug 2020 08:27:33 +0200 From: Peter Zijlstra To: Peter Oskolkov Cc: Mathieu Desnoyers , "Paul E . McKenney" , Boqun Feng , linux-kernel@vger.kernel.org, Paul Turner , Chris Kennelly , Peter Oskolkov Subject: Re: [PATCH 1/2 v3] rseq/membarrier: add MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ Message-ID: <20200811062733.GP3982@worktop.programming.kicks-ass.net> References: <20200811000959.2486636-1-posk@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200811000959.2486636-1-posk@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 10, 2020 at 05:09:58PM -0700, Peter Oskolkov wrote: > @@ -27,6 +35,12 @@ > > static void ipi_mb(void *info) > { The #ifdef wants to behere, otherwise you'll get a compile warning for !RSEQ builds. > + int *flags = info; > + > +#ifdef CONFIG_RSEQ > + if (flags && (*flags == MEMBARRIER_FLAG_RSEQ)) > + rseq_preempt(current); > +#endif > smp_mb(); /* IPIs should be serializing but paranoid. */ > } But yes, this looks much better. Mathieu did mention a few other points that I didn't see addressed: - he didn't like abusing the @flags syscall argument for a CPUid; - he wondered if we should support SYNC_CORE + RSEQ. Not sure we can easily change the syscall at this point, but the latter point could be addressed with something like this. --- Index: linux-2.6/kernel/sched/membarrier.c =================================================================== --- linux-2.6.orig/kernel/sched/membarrier.c +++ linux-2.6/kernel/sched/membarrier.c @@ -374,8 +374,26 @@ static int membarrier_register_private_e */ SYSCALL_DEFINE2(membarrier, int, cmd, int, flags) { + int cflags = 0, int cpuid = -1; + if (unlikely(flags) && cmd != MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ) return -EINVAL; + + if (cmd & (MEMBARRIER_CMD_PRIVATE_EXPEDITED | + MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE | + MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ)) { + + if (cmd & MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ) + cflags |= MEMBARRIER_FLAG_RSEQ; + + if (cmd & MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE) { + cflags |= MEMBARRIER_FLAG_SYNC_CORE; + cpuid = flags; + } + + cmd = MEMBARRIER_CMD_PRIVATE_EXPEDITED; + } + switch (cmd) { case MEMBARRIER_CMD_QUERY: { @@ -396,18 +414,16 @@ SYSCALL_DEFINE2(membarrier, int, cmd, in return membarrier_global_expedited(); case MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED: return membarrier_register_global_expedited(); - case MEMBARRIER_CMD_PRIVATE_EXPEDITED: - return membarrier_private_expedited(0, -1); case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED: return membarrier_register_private_expedited(0); - case MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE: - return membarrier_private_expedited(MEMBARRIER_FLAG_SYNC_CORE, -1); case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE: return membarrier_register_private_expedited(MEMBARRIER_FLAG_SYNC_CORE); - case MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ: - return membarrier_private_expedited(MEMBARRIER_FLAG_RSEQ, flags); case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ: return membarrier_register_private_expedited(MEMBARRIER_FLAG_RSEQ); + + case MEMBARRIER_CMD_PRIVATE_EXPEDITED: + return membarrier_private_expedited(cflags, cpuid); + default: return -EINVAL; }