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=-12.8 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=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 46C4BC4363A for ; Tue, 20 Oct 2020 13:47:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E202F206D9 for ; Tue, 20 Oct 2020 13:47:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.b="id7oikIS" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2407677AbgJTNra (ORCPT ); Tue, 20 Oct 2020 09:47:30 -0400 Received: from mail.efficios.com ([167.114.26.124]:43566 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2407620AbgJTNrV (ORCPT ); Tue, 20 Oct 2020 09:47:21 -0400 Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id 751912D91D0; Tue, 20 Oct 2020 09:47:20 -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 0s1hfb8zK3PH; Tue, 20 Oct 2020 09:47:20 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id A421F2D91CF; Tue, 20 Oct 2020 09:47:19 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com A421F2D91CF DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1603201639; bh=wdlHdXScqDBTUYMXWUj2Bb++1fuTmyvvGLKL/AUpDt8=; h=From:To:Date:Message-Id; b=id7oikISqN1YevT0zaWn3UwFRprlsLOPVMH+AlLldDo/Sji+tXSxS+McVCx3avrTb d3NRLdgUv9BPRAe9pO+okn/uCQfIgFlKqUqN5okWTaBM7CwnUJYyaMpZ64vzTphkPz T1jeGsHyO3g30ET+iYqgZo8yfhPBGqMpXWE0lZdkhL7fs2NiQbuD68idfkfRTCURxg 19VF0Q15DcDnReCiRhqo3xynRKFtkzkQ6pSymJT0HZ0RcjnFCjzFPQLTZJULJFBlRC P+Lq9kivDovP9BTUtlY1qJnBmII3GVvP/CD7a3Q+7onrEr4A8tMuNown9R/1VgJeh3 jEkb+9ZD43g8A== 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 iXbtnrNxZNGa; Tue, 20 Oct 2020 09:47:19 -0400 (EDT) Received: from localhost.localdomain (192-222-181-218.qc.cable.ebox.net [192.222.181.218]) by mail.efficios.com (Postfix) with ESMTPSA id 18AF12D939B; Tue, 20 Oct 2020 09:47:19 -0400 (EDT) From: Mathieu Desnoyers To: Peter Zijlstra , Boqun Feng Cc: linux-kernel@vger.kernel.org, Mathieu Desnoyers , Will Deacon , "Paul E . McKenney" , Nicholas Piggin , Andy Lutomirski , Andrew Morton Subject: [PATCH 2/3] sched: membarrier: cover kthread_use_mm (v4) Date: Tue, 20 Oct 2020 09:47:14 -0400 Message-Id: <20201020134715.13909-3-mathieu.desnoyers@efficios.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20201020134715.13909-1-mathieu.desnoyers@efficios.com> References: <20201020134715.13909-1-mathieu.desnoyers@efficios.com> 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. Now that membarrier_global_expedited can IPI kthreads, the scheduler also needs to update the runqueue's membarrier_state when entering lazy TLB state. Signed-off-by: Mathieu Desnoyers Cc: Peter Zijlstra (Intel) Cc: Boqun Feng Cc: Will Deacon Cc: Paul E. McKenney Cc: Nicholas Piggin Cc: Andy Lutomirski Cc: Andrew Morton --- Changes since v1: - Add WARN_ON_ONCE(current->mm) in play_idle_precise (PeterZ), - Use smp_mb__after_spinlock rather than smp_mb after task_lock. Changes since v2: - Update the rq's membarrier state on kthread use/unuse mm, - The scheduler must use membarrier_switch_mm for lazy TLB case as well, now that global expedited membarrier IPIs kthreads. Changes since v3: - Revert back to not using membarrier_switch_mm for lazy TLB case. This is made OK by ensuring that the global expedited membarrier only skips kthreads which have a NULL mm, so it only skips kthreads which are in lazy TLB mode. --- kernel/kthread.c | 21 +++++++++++++++++++++ kernel/sched/idle.c | 1 + kernel/sched/membarrier.c | 7 +++---- 3 files changed, 25 insertions(+), 4 deletions(-) diff --git a/kernel/kthread.c b/kernel/kthread.c index 3edaa380dc7b..a396734d31f3 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -1248,6 +1248,7 @@ void kthread_use_mm(struct mm_struct *mm) tsk->active_mm = mm; } tsk->mm = mm; + membarrier_update_current_mm(mm); switch_mm_irqs_off(active_mm, mm, tsk); local_irq_enable(); task_unlock(tsk); @@ -1255,8 +1256,19 @@ 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(), or explicitly with smp_mb(). + */ if (active_mm != mm) mmdrop(active_mm); + else + smp_mb(); to_kthread(tsk)->oldfs = force_uaccess_begin(); } @@ -1276,9 +1288,18 @@ void kthread_unuse_mm(struct mm_struct *mm) force_uaccess_end(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__after_spinlock(); sync_mm_rss(mm); local_irq_disable(); tsk->mm = NULL; + membarrier_update_current_mm(NULL); /* active_mm is still 'mm' */ enter_lazy_tlb(mm, tsk); local_irq_enable(); diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c index f324dc36fc43..f0d81a5ea471 100644 --- a/kernel/sched/idle.c +++ b/kernel/sched/idle.c @@ -338,6 +338,7 @@ void play_idle_precise(u64 duration_ns, u64 latency_ns) WARN_ON_ONCE(!(current->flags & PF_KTHREAD)); WARN_ON_ONCE(!(current->flags & PF_NO_SETAFFINITY)); WARN_ON_ONCE(!duration_ns); + WARN_ON_ONCE(current->mm); rcu_sleep_check(); preempt_disable(); diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c index 8bc8b8a888b7..8b93b6844901 100644 --- a/kernel/sched/membarrier.c +++ b/kernel/sched/membarrier.c @@ -113,12 +113,11 @@ static int membarrier_global_expedited(void) 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 a kernel thread which is not using + * a task mm. */ p = rcu_dereference(cpu_rq(cpu)->curr); - if (p->flags & PF_KTHREAD) + if (!p->mm) continue; __cpumask_set_cpu(cpu, tmpmask); -- 2.17.1