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=-2.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 92831C6778A for ; Sun, 1 Jul 2018 17:52:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 57FC725796 for ; Sun, 1 Jul 2018 17:52:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 57FC725796 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linuxfoundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934128AbeGARw0 (ORCPT ); Sun, 1 Jul 2018 13:52:26 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:35134 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030585AbeGAQcP (ORCPT ); Sun, 1 Jul 2018 12:32:15 -0400 Received: from localhost (LFbn-1-12247-202.w90-92.abo.wanadoo.fr [90.92.61.202]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 1017349B; Sun, 1 Jul 2018 16:32:14 +0000 (UTC) From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Mike Marciniszyn , Sebastian Sanchez , Dennis Dalessandro , Doug Ledford Subject: [PATCH 4.14 068/157] IB/hfi1: Optimize kthread pointer locking when queuing CQ entries Date: Sun, 1 Jul 2018 18:22:20 +0200 Message-Id: <20180701160856.016169974@linuxfoundation.org> X-Mailer: git-send-email 2.18.0 In-Reply-To: <20180701160852.287307684@linuxfoundation.org> References: <20180701160852.287307684@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Sebastian Sanchez commit af8aab71370a692eaf7e7969ba5b1a455ac20113 upstream. All threads queuing CQ entries on different CQs are unnecessarily synchronized by a spin lock to check if the CQ kthread worker hasn't been destroyed before queuing an CQ entry. The lock used in 6efaf10f163d ("IB/rdmavt: Avoid queuing work into a destroyed cq kthread worker") is a device global lock and will have poor performance at scale as completions are entered from a large number of CPUs. Convert to use RCU where the read side of RCU is rvt_cq_enter() to determine that the worker is alive prior to triggering the completion event. Apply write side RCU semantics in rvt_driver_cq_init() and rvt_cq_exit(). Fixes: 6efaf10f163d ("IB/rdmavt: Avoid queuing work into a destroyed cq kthread worker") Cc: # 4.14.x Reviewed-by: Mike Marciniszyn Signed-off-by: Sebastian Sanchez Signed-off-by: Dennis Dalessandro Signed-off-by: Doug Ledford Signed-off-by: Greg Kroah-Hartman --- drivers/infiniband/sw/rdmavt/cq.c | 31 +++++++++++++++++++------------ include/rdma/rdma_vt.h | 2 +- 2 files changed, 20 insertions(+), 13 deletions(-) --- a/drivers/infiniband/sw/rdmavt/cq.c +++ b/drivers/infiniband/sw/rdmavt/cq.c @@ -121,17 +121,20 @@ void rvt_cq_enter(struct rvt_cq *cq, str if (cq->notify == IB_CQ_NEXT_COMP || (cq->notify == IB_CQ_SOLICITED && (solicited || entry->status != IB_WC_SUCCESS))) { + struct kthread_worker *worker; + /* * This will cause send_complete() to be called in * another thread. */ - spin_lock(&cq->rdi->n_cqs_lock); - if (likely(cq->rdi->worker)) { + rcu_read_lock(); + worker = rcu_dereference(cq->rdi->worker); + if (likely(worker)) { cq->notify = RVT_CQ_NONE; cq->triggered++; - kthread_queue_work(cq->rdi->worker, &cq->comptask); + kthread_queue_work(worker, &cq->comptask); } - spin_unlock(&cq->rdi->n_cqs_lock); + rcu_read_unlock(); } spin_unlock_irqrestore(&cq->lock, flags); @@ -513,7 +516,7 @@ int rvt_driver_cq_init(struct rvt_dev_in int cpu; struct kthread_worker *worker; - if (rdi->worker) + if (rcu_access_pointer(rdi->worker)) return 0; spin_lock_init(&rdi->n_cqs_lock); @@ -525,7 +528,7 @@ int rvt_driver_cq_init(struct rvt_dev_in return PTR_ERR(worker); set_user_nice(worker->task, MIN_NICE); - rdi->worker = worker; + RCU_INIT_POINTER(rdi->worker, worker); return 0; } @@ -537,15 +540,19 @@ void rvt_cq_exit(struct rvt_dev_info *rd { struct kthread_worker *worker; - /* block future queuing from send_complete() */ - spin_lock_irq(&rdi->n_cqs_lock); - worker = rdi->worker; + if (!rcu_access_pointer(rdi->worker)) + return; + + spin_lock(&rdi->n_cqs_lock); + worker = rcu_dereference_protected(rdi->worker, + lockdep_is_held(&rdi->n_cqs_lock)); if (!worker) { - spin_unlock_irq(&rdi->n_cqs_lock); + spin_unlock(&rdi->n_cqs_lock); return; } - rdi->worker = NULL; - spin_unlock_irq(&rdi->n_cqs_lock); + RCU_INIT_POINTER(rdi->worker, NULL); + spin_unlock(&rdi->n_cqs_lock); + synchronize_rcu(); kthread_destroy_worker(worker); } --- a/include/rdma/rdma_vt.h +++ b/include/rdma/rdma_vt.h @@ -409,7 +409,7 @@ struct rvt_dev_info { spinlock_t pending_lock; /* protect pending mmap list */ /* CQ */ - struct kthread_worker *worker; /* per device cq worker */ + struct kthread_worker __rcu *worker; /* per device cq worker */ u32 n_cqs_allocated; /* number of CQs allocated for device */ spinlock_t n_cqs_lock; /* protect count of in use cqs */