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=-19.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,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 4F957C48BDF for ; Wed, 16 Jun 2021 03:21:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 38BB960FE6 for ; Wed, 16 Jun 2021 03:21:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230411AbhFPDXk (ORCPT ); Tue, 15 Jun 2021 23:23:40 -0400 Received: from mail.kernel.org ([198.145.29.99]:42832 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230175AbhFPDXY (ORCPT ); Tue, 15 Jun 2021 23:23:24 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id CBB8B613B9; Wed, 16 Jun 2021 03:21:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1623813678; bh=q8HZKPxpOM/5sR9eo6stVaodXdedvsUQjQBqGomYFTM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=PVgslUPvnm4dag5figXFo7ByhJdeLViFstuVBA+2bOh0q+jJHFNjAdQ7OpvTwfLO/ e3N/qUhm7guRAWmGpjwLX9hfG3lnJpHOriP8yMB7h7o+8XSPrdeWGBjmnx4GETkErX jGk2ZjznvfntfeJKtdGpxUnGlbz+4wNCAmbFxySDGlhuJPuIteVF1+Nkxr1WP6Wjwv wVxUjteZpKgHgRynJAVOte0dGblqJ8Ae3qokLj6BiRa9XkfLj2r5FtpB74jgw8ZY5+ ZVrFcz4GKe0g0AhBux8EONMOlllRPzI1zDXWURMqMn27BBLuiAM7SOqCIN1oYlj2LX vUkKcug1HeGlw== From: Andy Lutomirski To: x86@kernel.org Cc: Dave Hansen , LKML , linux-mm@kvack.org, Andrew Morton , Andy Lutomirski , Mathieu Desnoyers , Nicholas Piggin , Peter Zijlstra Subject: [PATCH 5/8] membarrier, kthread: Use _ONCE accessors for task->mm Date: Tue, 15 Jun 2021 20:21:10 -0700 Message-Id: <74ace142f48db7d0e71b05b5ace72bfe8e0a2652.1623813516.git.luto@kernel.org> X-Mailer: git-send-email 2.31.1 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org membarrier reads cpu_rq(remote cpu)->curr->mm without locking. Use READ_ONCE() and WRITE_ONCE() to remove the data races. Cc: Mathieu Desnoyers Cc: Nicholas Piggin Cc: Peter Zijlstra Signed-off-by: Andy Lutomirski --- fs/exec.c | 2 +- kernel/kthread.c | 4 ++-- kernel/sched/membarrier.c | 6 +++--- 3 files changed, 6 insertions(+), 6 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index 18594f11c31f..2e63dea83411 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1007,7 +1007,7 @@ static int exec_mmap(struct mm_struct *mm) local_irq_disable(); active_mm = tsk->active_mm; tsk->active_mm = mm; - tsk->mm = mm; + WRITE_ONCE(tsk->mm, mm); /* membarrier reads this without locks */ /* * This prevents preemption while active_mm is being loaded and * it and mm are being updated, which could cause problems for diff --git a/kernel/kthread.c b/kernel/kthread.c index 8275b415acec..4962794e02d5 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -1322,7 +1322,7 @@ void kthread_use_mm(struct mm_struct *mm) mmgrab(mm); tsk->active_mm = mm; } - tsk->mm = mm; + WRITE_ONCE(tsk->mm, mm); /* membarrier reads this without locks */ membarrier_update_current_mm(mm); switch_mm_irqs_off(active_mm, mm, tsk); membarrier_finish_switch_mm(atomic_read(&mm->membarrier_state)); @@ -1363,7 +1363,7 @@ void kthread_unuse_mm(struct mm_struct *mm) smp_mb__after_spinlock(); sync_mm_rss(mm); local_irq_disable(); - tsk->mm = NULL; + WRITE_ONCE(tsk->mm, NULL); /* membarrier reads this without locks */ membarrier_update_current_mm(NULL); /* active_mm is still 'mm' */ enter_lazy_tlb(mm, tsk); diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c index 3173b063d358..c32c32a2441e 100644 --- a/kernel/sched/membarrier.c +++ b/kernel/sched/membarrier.c @@ -410,7 +410,7 @@ static int membarrier_private_expedited(int flags, int cpu_id) goto out; rcu_read_lock(); p = rcu_dereference(cpu_rq(cpu_id)->curr); - if (!p || p->mm != mm) { + if (!p || READ_ONCE(p->mm) != mm) { rcu_read_unlock(); goto out; } @@ -423,7 +423,7 @@ static int membarrier_private_expedited(int flags, int cpu_id) struct task_struct *p; p = rcu_dereference(cpu_rq(cpu)->curr); - if (p && p->mm == mm) + if (p && READ_ONCE(p->mm) == mm) __cpumask_set_cpu(cpu, tmpmask); } rcu_read_unlock(); @@ -521,7 +521,7 @@ static int sync_runqueues_membarrier_state(struct mm_struct *mm) struct task_struct *p; p = rcu_dereference(rq->curr); - if (p && p->mm == mm) + if (p && READ_ONCE(p->mm) == mm) __cpumask_set_cpu(cpu, tmpmask); } rcu_read_unlock(); -- 2.31.1