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=-13.1 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT autolearn=unavailable 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 7351AC433E3 for ; Tue, 28 Jul 2020 16:00:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4BA2A2053B for ; Tue, 28 Jul 2020 16:00:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.b="ssLyZp/v" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731229AbgG1QAR (ORCPT ); Tue, 28 Jul 2020 12:00:17 -0400 Received: from mail.efficios.com ([167.114.26.124]:44370 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730994AbgG1QAQ (ORCPT ); Tue, 28 Jul 2020 12:00:16 -0400 Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id D2CF129A886; Tue, 28 Jul 2020 12:00:14 -0400 (EDT) Received: from mail.efficios.com ([127.0.0.1]) by localhost (mail03.efficios.com [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id qn_CIEv5heer; Tue, 28 Jul 2020 12:00:14 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id 936D829A618; Tue, 28 Jul 2020 12:00:14 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com 936D829A618 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1595952014; bh=2xoJecq6SiKChi0NlXRlWBK3yJHwYnLJVWhwBhqc12g=; h=From:To:Date:Message-Id; b=ssLyZp/vmIqNOapsb0P3FDyt/rFEI83M16WIMxDldCWZ8zgkrASLmG6qjz2JZLEPQ XaXx2KF1UnI54yKqapwgNQWUyiRS7Z0SDI2kDsQTSUrS+1Igk9iAPRWq4tnAAXP7SW JTmbJD1NlpLih6qZJQqYtFti5TzmchgXPc/Inhp+qajfGyYmeL3UJySlO3fqGF0HV1 dplwaPrRV11zR1AiDRQs8e8S72m/jcU+HPdISAHLUug4uOq+ePEcLip9tcUgoaMjc1 kXnv3h6crcvgbjUA70jqzvfJ6MEEB+kYx8NwPISPJ70o3RBdKZh4wStZH55hL1mJPR GklCkXhuWN35g== X-Virus-Scanned: amavisd-new at efficios.com Received: from mail.efficios.com ([127.0.0.1]) by localhost (mail03.efficios.com [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id LNYLVUcXcOdE; Tue, 28 Jul 2020 12:00:14 -0400 (EDT) Received: from thinkos.etherlink (unknown [192.222.236.144]) by mail.efficios.com (Postfix) with ESMTPSA id 67F2729A728; Tue, 28 Jul 2020 12:00:14 -0400 (EDT) From: Mathieu Desnoyers To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, Mathieu Desnoyers , Will Deacon , "Paul E . McKenney" , Nicholas Piggin , Andy Lutomirski , Andrew Morton Subject: [RFC PATCH 2/2] sched: membarrier: cover kthread_use_mm Date: Tue, 28 Jul 2020 12:00:10 -0400 Message-Id: <20200728160010.3314-2-mathieu.desnoyers@efficios.com> X-Mailer: git-send-email 2.11.0 In-Reply-To: <20200728160010.3314-1-mathieu.desnoyers@efficios.com> References: <20200728160010.3314-1-mathieu.desnoyers@efficios.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Add comments and memory barrier to kthread_use_mm and kthread_unuse_mm to allow the effect of membarrier(2) to apply to kthreads accessing user-space memory as well. Given that no prior kthread use this guarantee and that it only affects kthreads, adding this guarantee does not affect user-space ABI. Refine the check in membarrier_global_expedited to exclude runqueues running the idle thread rather than all kthreads from the IPI cpumask. This patch applies on top of this patch from Peter Zijlstra: "mm: fix kthread_use_mm() vs TLB invalidate" currently in Andrew Morton's tree. Signed-off-by: Mathieu Desnoyers Cc: Peter Zijlstra (Intel) Cc: Will Deacon Cc: Paul E. McKenney Cc: Nicholas Piggin Cc: Andy Lutomirski Cc: Andrew Morton --- kernel/kthread.c | 19 +++++++++++++++++++ kernel/sched/membarrier.c | 8 ++------ 2 files changed, 21 insertions(+), 6 deletions(-) diff --git a/kernel/kthread.c b/kernel/kthread.c index 48925b17920e..ef2435517f14 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -1258,8 +1258,19 @@ void kthread_use_mm(struct mm_struct *mm) finish_arch_post_lock_switch(); #endif + /* + * When a kthread starts 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 storing to tsk->mm, before accessing + * user-space memory. A full memory barrier for membarrier + * {PRIVATE,GLOBAL}_EXPEDITED is implicitly provided by + * mmdrop(). + */ if (active_mm != mm) mmdrop(active_mm); + else + smp_mb(); to_kthread(tsk)->oldfs = get_fs(); set_fs(USER_DS); @@ -1280,6 +1291,14 @@ void kthread_unuse_mm(struct mm_struct *mm) set_fs(to_kthread(tsk)->oldfs); 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(); tsk->mm = NULL; diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c index 168479a7d61b..8a294483074d 100644 --- a/kernel/sched/membarrier.c +++ b/kernel/sched/membarrier.c @@ -100,13 +100,9 @@ static int membarrier_global_expedited(void) MEMBARRIER_STATE_GLOBAL_EXPEDITED)) continue; - /* - * Skip the CPU if it runs a kernel thread. The scheduler - * leaves the prior task mm in place as an optimization when - * scheduling a kthread. - */ + /* Skip the CPU if it runs the idle thread. */ p = rcu_dereference(cpu_rq(cpu)->curr); - if (p->flags & PF_KTHREAD) + if (is_idle_task(p)) continue; __cpumask_set_cpu(cpu, tmpmask); -- 2.11.0