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=-12.9 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 82604C4363D for ; Thu, 24 Sep 2020 17:25:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 32832206D9 for ; Thu, 24 Sep 2020 17:25:32 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.b="YKxH2sen" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728709AbgIXRZb (ORCPT ); Thu, 24 Sep 2020 13:25:31 -0400 Received: from mail.efficios.com ([167.114.26.124]:53580 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728548AbgIXRZT (ORCPT ); Thu, 24 Sep 2020 13:25:19 -0400 Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id 268722D64DF; Thu, 24 Sep 2020 13:25:18 -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 x7T-MVb3KWCP; Thu, 24 Sep 2020 13:25:17 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id 91F302D6819; Thu, 24 Sep 2020 13:25:17 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com 91F302D6819 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1600968317; bh=zLxn7FGoPJYghx49QThG3MR35b326LMYvjG0XfsBwp8=; h=From:To:Date:Message-Id; b=YKxH2senveOrLhPR8u+TuNB+9UE0ZjUmEAbMeOEwmdwLAWJTzcaOeAxMwPe47LCWi DN5bkSvAwZuyniIoXgz4lHwuAxMcfc/rjpnP+U3bg9/SlN8RgaC3pYW85jjKiLDtMl FGfch6M/1Mvtrg38wDuu1G31sNmOYjqZAF3j8wr0y9P5KNL4me/dSy1luZemsptOVC L3dbuv3cttm42HBPtOvU7pSoAP3gsVkwQicI3XYla5LFXwKGBizyae3VeMDviUHm/g WstrEADUNpq0dXBnQIHu0NN/zwh5ikOEgDsI6QxiXACMGw0eKlGXTUAghlewiJ1Xlj +lttr8BIZeySg== 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 PgRD4eLp1GvJ; Thu, 24 Sep 2020 13:25:17 -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 672BD2D66D0; Thu, 24 Sep 2020 13:25:17 -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: [RFC PATCH 2/3] sched: membarrier: cover kthread_use_mm (v3) Date: Thu, 24 Sep 2020 13:25:07 -0400 Message-Id: <20200924172508.8724-3-mathieu.desnoyers@efficios.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20200924172508.8724-1-mathieu.desnoyers@efficios.com> References: <20200924172508.8724-1-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. --- kernel/kthread.c | 21 +++++++++++++++++++++ kernel/sched/core.c | 3 ++- kernel/sched/idle.c | 1 + kernel/sched/membarrier.c | 8 ++------ kernel/sched/sched.h | 5 +++-- 5 files changed, 29 insertions(+), 9 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/core.c b/kernel/sched/core.c index 2d95dc3f4644..bab6f4f2809f 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3736,6 +3736,8 @@ context_switch(struct rq *rq, struct task_struct *prev, */ arch_start_context_switch(prev); + membarrier_switch_mm(rq, prev->mm, next->mm); + /* * kernel -> kernel lazy + transfer active * user -> kernel lazy + mmgrab() active @@ -3752,7 +3754,6 @@ context_switch(struct rq *rq, struct task_struct *prev, else prev->active_mm = NULL; } else { // to user - membarrier_switch_mm(rq, prev->active_mm, next->mm); /* * sys_membarrier() requires an smp_mb() between setting * rq->curr / membarrier_switch_mm() and returning to userspace. 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..e5246580201b 100644 --- a/kernel/sched/membarrier.c +++ b/kernel/sched/membarrier.c @@ -112,13 +112,9 @@ 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); diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 28709f6b0975..d884959d4280 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -2592,12 +2592,13 @@ static inline void membarrier_switch_mm(struct rq *rq, struct mm_struct *prev_mm, struct mm_struct *next_mm) { - int membarrier_state; + int membarrier_state = 0; if (prev_mm == next_mm) return; - membarrier_state = atomic_read(&next_mm->membarrier_state); + if (next_mm) + membarrier_state = atomic_read(&next_mm->membarrier_state); if (READ_ONCE(rq->membarrier_state) == membarrier_state) return; -- 2.17.1