Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1946496AbbEVReA (ORCPT ); Fri, 22 May 2015 13:34:00 -0400 Received: from mail-ig0-f170.google.com ([209.85.213.170]:35510 "EHLO mail-ig0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1945960AbbEVRd7 (ORCPT ); Fri, 22 May 2015 13:33:59 -0400 MIME-Version: 1.0 In-Reply-To: References: <1432253553-17045-1-git-send-email-parav.pandit@avagotech.com> Date: Fri, 22 May 2015 23:03:58 +0530 Message-ID: Subject: Re: [PATCH] NVMe: Avoid interrupt disable during queue init. From: Parav Pandit To: Keith Busch Cc: linux-nvme@lists.infradead.org, Matthew Wilcox , Jens Axboe , linux-kernel@vger.kernel.org Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1483 Lines: 45 On Fri, May 22, 2015 at 10:37 PM, Keith Busch wrote: > On Fri, 22 May 2015, Parav Pandit wrote: >> >> On Fri, May 22, 2015 at 9:53 PM, Keith Busch >> wrote: >>> >>> A memory barrier before incrementing the dev->queue_count (and assigning >>> the pointer in the array before that) should address this concern. >> >> >> Sure. mb() will solve the publisher side problem. RCU is wrapper around >> mb(). >> However mb() doesn't solve the issue of q_lock variable getting >> fetched before if (!nvmeq) condition being executed, by value >> compilation optimizations in nvme_kthread(). > > > Eh? The value of dev->queue_count prevents the thread's for-loop from > iterating that nvmeq before the q_lock is initialized. I agree to it that nvmeq won't be null after mb(); That alone is not sufficient. What I have proposed in previous email is, Converting, struct nvme_queue *nvmeq = dev->queues[i]; if (!nvmeq) continue; spin_lock_irq(nvmeq->q_lock); to replace with, struct nvme_queue *nvmeq = rcu_dereference(dev->queues[i]); if (!nvmeq) continue; spin_lock_irq(nvmeq->q_lock); This will prevent fetching content of q_lock before checking for NULL condition. Classic usage or RCU. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/