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=-5.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 E193FC3A5A7 for ; Wed, 4 Sep 2019 11:28:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B86BA22DBF for ; Wed, 4 Sep 2019 11:28:39 +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="mYBA1iC8" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729493AbfIDL2j (ORCPT ); Wed, 4 Sep 2019 07:28:39 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:53658 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727351AbfIDL2i (ORCPT ); Wed, 4 Sep 2019 07:28:38 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=ylEYuetQjRSTjE1zCpDEWeA2Rhzr2VKqQz1x4DO54Ds=; b=mYBA1iC87c0Wifn9jMnoJAkC9 GBfiEPqEwwGDBj33t+snQ/+CE2BgmzBICVrwMZ/I/KZIoatF8uOW9HqlmLwdjJ/xfpLMg+IzrD/9Q O4eOnnVjfIBIG/ELqQvl0Mh8Fc5r1e/ZmAX8b/KurwtBvBD1n1kTlUnHigPPjr2f5NoEpDIrh6gOH woAnK1XrgwIAszYsd6wxKP09VDRfBk/W8Bjwe/m3RcX3d1JbW8zSYP1GyN9gmGiCy3RxLNZ6kzqZw ztrGuHQijWzK5jAnJDN52lYQPc45Lh3HbkxDQHM+OEcXK6UH96aFFH1IEwcxFuVm3qz8K1zvWV5rO zOz2jw7zQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92 #3 (Red Hat Linux)) id 1i5TSZ-0004nM-4W; Wed, 04 Sep 2019 11:28:23 +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 5AF8D306027; Wed, 4 Sep 2019 13:27:43 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id D348529C0A898; Wed, 4 Sep 2019 13:28:19 +0200 (CEST) Date: Wed, 4 Sep 2019 13:28:19 +0200 From: Peter Zijlstra To: Mathieu Desnoyers Cc: paulmck , Linus Torvalds , linux-kernel , Oleg Nesterov , "Eric W. Biederman" , "Russell King, ARM Linux" , Chris Metcalf , Chris Lameter , Kirill Tkhai , Mike Galbraith , Thomas Gleixner , Ingo Molnar Subject: Re: [RFC PATCH 1/2] Fix: sched/membarrier: p->mm->membarrier_state racy load Message-ID: <20190904112819.GD2349@hirez.programming.kicks-ass.net> References: <20190903201135.1494-1-mathieu.desnoyers@efficios.com> <20190903202434.GX2349@hirez.programming.kicks-ass.net> <1029906102.725.1567543307658.JavaMail.zimbra@efficios.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1029906102.725.1567543307658.JavaMail.zimbra@efficios.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 Tue, Sep 03, 2019 at 04:41:47PM -0400, Mathieu Desnoyers wrote: > As discussed on IRC, one alternative for the multi-threaded case would > be to grab the task list lock and iterate over all existing tasks to > set the bit, so we don't have to touch an extra cache line from the > scheduler. > > In order to keep the speed of the common single-threaded library > constructor common case fast, we simply set the bit in the current > task struct, and rely on clone() propagating the flag to children > threads (which it already does). Something like the completely untested thing below. And yes, that do_each_thread/while_each_thread thing is unfortunate and yuck too, but supposedly that's a slow path not many people are expected to hit anyway, right? --- include/linux/sched.h | 4 ++++ kernel/sched/membarrier.c | 20 +++++++++++++++++--- 2 files changed, 21 insertions(+), 3 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 33b310a826d7..dbafafb8ef40 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1136,6 +1136,10 @@ struct task_struct { unsigned long numa_pages_migrated; #endif /* CONFIG_NUMA_BALANCING */ +#ifdef CONFIG_MEMBARRIER + atomic_t membarrier_state; +#endif + #ifdef CONFIG_RSEQ struct rseq __user *rseq; u32 rseq_sig; diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c index aa8d75804108..961f6affbf38 100644 --- a/kernel/sched/membarrier.c +++ b/kernel/sched/membarrier.c @@ -72,8 +72,8 @@ static int membarrier_global_expedited(void) rcu_read_lock(); p = task_rcu_dereference(&cpu_rq(cpu)->curr); - if (p && p->mm && (atomic_read(&p->mm->membarrier_state) & - MEMBARRIER_STATE_GLOBAL_EXPEDITED)) { + if (p && (atomic_read(&p->membarrier_state) & + MEMBARRIER_STATE_GLOBAL_EXPEDITED)) { if (!fallback) __cpumask_set_cpu(cpu, tmpmask); else @@ -185,7 +185,9 @@ static int membarrier_register_global_expedited(void) if (atomic_read(&mm->membarrier_state) & MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY) return 0; + atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED, &mm->membarrier_state); + atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED, &p->membarrier_state); if (atomic_read(&mm->mm_users) == 1 && get_nr_threads(p) == 1) { /* * For single mm user, single threaded process, we can @@ -196,6 +198,17 @@ static int membarrier_register_global_expedited(void) */ smp_mb(); } else { + struct task_struct *g, *t; + + read_lock(&tasklist_lock); + do_each_thread(g, t) { + if (t->mm == mm) { + atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED, + &t->membarrier_state); + } + } while_each_thread(g, t); + read_unlock(&tasklist_lock); + /* * For multi-mm user threads, we need to ensure all * future scheduler executions will observe the new @@ -229,9 +242,10 @@ static int membarrier_register_private_expedited(int flags) if (atomic_read(&mm->membarrier_state) & state) return 0; atomic_or(MEMBARRIER_STATE_PRIVATE_EXPEDITED, &mm->membarrier_state); - if (flags & MEMBARRIER_FLAG_SYNC_CORE) + if (flags & MEMBARRIER_FLAG_SYNC_CORE) { atomic_or(MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE, &mm->membarrier_state); + } if (!(atomic_read(&mm->mm_users) == 1 && get_nr_threads(p) == 1)) { /* * Ensure all future scheduler executions will observe the