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=-14.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 97D45C2D0A3 for ; Thu, 29 Oct 2020 10:52:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2E3AC20731 for ; Thu, 29 Oct 2020 10:52:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="Ji3v+x2m"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="UWNdZhst" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727354AbgJ2Kwk (ORCPT ); Thu, 29 Oct 2020 06:52:40 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:60762 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726992AbgJ2Kvt (ORCPT ); Thu, 29 Oct 2020 06:51:49 -0400 Date: Thu, 29 Oct 2020 10:51:46 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1603968707; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=773iFDmIRCiK7AimWc3nu+vIYasWQaqR8+9ya7hBwGE=; b=Ji3v+x2mk3QIIAlLppMDoNk4E+asf+B7jgQLs6VFVn9hm31D4EuvIuLg6FvoI3Fz9aH6bL oG3/dxgzFGmqGymVZBpt/Bwzw2P4N5J2viiXLYrzc4dua6vhMZ4FogaYx8l1kTM89f5OsU YlyFmvU+DWLb2jRQs50pFeq14Letquywg/VZrLVkvY2MDcTMZEJ9GTIrJhceSjvZ4SPfvP 3dIrvks6sg99cLClkQqfGZ0g4oSul+R4/Xf4sRs1f77Jt/BhIhx+RVlyiAcjZEJ72QvwDJ jLfYWX80BC7D2BqnQalDXQt1E+dC4vaNYdtQPzGepTNBA29c+xDTUolnS8BycA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1603968707; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=773iFDmIRCiK7AimWc3nu+vIYasWQaqR8+9ya7hBwGE=; b=UWNdZhstEn5M89EuLH0+7bsqOHq+MB6mKbSiu3gbbl629dEjmWVin+XTN6aEo3TXaHoSGt ogOK1W5t6jPeMjDA== From: "tip-bot2 for Mathieu Desnoyers" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: sched/core] sched: membarrier: cover kthread_use_mm (v4) Cc: Mathieu Desnoyers , "Peter Zijlstra (Intel)" , x86 , LKML In-Reply-To: <20201020134715.13909-3-mathieu.desnoyers@efficios.com> References: <20201020134715.13909-3-mathieu.desnoyers@efficios.com> MIME-Version: 1.0 Message-ID: <160396870681.397.6742175131689946098.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the sched/core branch of tip: Commit-ID: 618758ed3a4f7d790414d020b362111748ebbf9f Gitweb: https://git.kernel.org/tip/618758ed3a4f7d790414d020b362111748ebbf9f Author: Mathieu Desnoyers AuthorDate: Tue, 20 Oct 2020 09:47:14 -04:00 Committer: Peter Zijlstra CommitterDate: Thu, 29 Oct 2020 11:00:31 +01:00 sched: membarrier: cover kthread_use_mm (v4) 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 Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20201020134715.13909-3-mathieu.desnoyers@efficios.com --- 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 e29773c..481428f 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 24d0ee2..846743e 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 aac3292..f223f35 100644 --- a/kernel/sched/membarrier.c +++ b/kernel/sched/membarrier.c @@ -126,12 +126,11 @@ 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);