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=-3.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 5E403C433DF for ; Tue, 4 Aug 2020 17:03:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 46602207FC for ; Tue, 4 Aug 2020 17:03:37 +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="CwCGk+Hs" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728048AbgHDRDg (ORCPT ); Tue, 4 Aug 2020 13:03:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52642 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728412AbgHDRCA (ORCPT ); Tue, 4 Aug 2020 13:02:00 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BBA6FC06174A for ; Tue, 4 Aug 2020 10:01:58 -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=ZJzXwOxbCfW8r8F6D6OIBH2hwsyGZnD1BkGyF7iIWDw=; b=CwCGk+Hs8UrOvgV3xxite97qfY PQAryBv0z8bbjhJ0/ylCabUh7eBXLJx3/xTWSb9Sj04b2mmOrMfn0ZDhN+b+W2t+OoOowvFJNzvc1 DiDEuHL3GqviNbY6ZKk5BPHtuD/r5itHHrF3UBzSdUsk4nAmYawx45aM1j3+4PQS0UKQTOM9mM8Ta d6WtctMWpFZCZK8pmrO/WivExlSrj+cGaOi739Zt85BR0VzpvRZW4AGOHDgophJR2uVGiyo21q1Sy GMQbRKqx6Qe7xzIi5iup6AcN+9xpp6s+ltu4XMS1r+lam8+Mmhqx1J7H3W+dXAAyKVW1xMvJc8qm2 yRjUs5mA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1k30K2-000535-UI; Tue, 04 Aug 2020 17:01:55 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id AAC1E301A66; Tue, 4 Aug 2020 19:01:53 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 81A032B90EB46; Tue, 4 Aug 2020 19:01:53 +0200 (CEST) Date: Tue, 4 Aug 2020 19:01:53 +0200 From: peterz@infradead.org To: Mathieu Desnoyers Cc: linux-kernel , Will Deacon , paulmck , Nicholas Piggin , Andy Lutomirski , Andrew Morton Subject: Re: [RFC PATCH 2/2] sched: membarrier: cover kthread_use_mm Message-ID: <20200804170153.GO2657@hirez.programming.kicks-ass.net> References: <20200728160010.3314-1-mathieu.desnoyers@efficios.com> <20200728160010.3314-2-mathieu.desnoyers@efficios.com> <20200804145145.GM2657@hirez.programming.kicks-ass.net> <1708074166.39992.1596553173337.JavaMail.zimbra@efficios.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1708074166.39992.1596553173337.JavaMail.zimbra@efficios.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 04, 2020 at 10:59:33AM -0400, Mathieu Desnoyers wrote: > ----- On Aug 4, 2020, at 10:51 AM, Peter Zijlstra peterz@infradead.org wrote: > > On Tue, Jul 28, 2020 at 12:00:10PM -0400, Mathieu Desnoyers wrote: > >> task_lock(tsk); > >> + /* > >> + * When a kthread stops operating on an address space, the loop > >> + * in membarrier_{private,global}_expedited() may not observe > >> + * that tsk->mm, and not issue an IPI. Membarrier requires a > >> + * memory barrier after accessing user-space memory, before > >> + * clearing tsk->mm. > >> + */ > >> + smp_mb(); > >> sync_mm_rss(mm); > >> local_irq_disable(); > > > > Would it make sense to put the smp_mb() inside the IRQ disable region? > > I've initially placed it right after task_lock so we could eventually > have a smp_mb__after_non_raw_spinlock or something with a much better naming, > which would allow removing the extra barrier when it is implied by the > spinlock. Oh, right, fair enough. I'll go think about if smp_mb__after_spinlock() will work for mutexes too. It basically needs to upgrade atomic*_acquire() to smp_mb(). So that's all architectures that have their own _acquire() and an actual smp_mb__after_atomic(). Which, from the top of my head are only arm64, power and possibly riscv. And if I then git-grep smp_mb__after_spinlock, all those seem to be covered. But let me do a better audit..