From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753553AbeENM5a (ORCPT ); Mon, 14 May 2018 08:57:30 -0400 Received: from mx2.suse.de ([195.135.220.15]:49400 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752897AbeENM53 (ORCPT ); Mon, 14 May 2018 08:57:29 -0400 Date: Mon, 14 May 2018 14:57:25 +0200 From: Johannes Thumshirn To: Christoph Hellwig Cc: Keith Busch , Sagi Grimberg , Linux Kernel Mailinglist , Linux NVMe Mailinglist , Hannes Reinecke , Christoph Hellwig , paulmck@linux.vnet.ibm.com Subject: Re: [PATCH] nvme: fix lockdep warning in nvme_mpath_clear_current_path Message-ID: <20180514125725.uobtf2nf4corisea@linux-x5ow.site> References: <20180514121312.13624-1-jthumshirn@suse.de> <20180514124230.GA654@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20180514124230.GA654@infradead.org> User-Agent: NeoMutt/20170912 (1.9.0) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 14, 2018 at 05:42:30AM -0700, Christoph Hellwig wrote: > > extern unsigned int nvme_io_timeout; > > #define NVME_IO_TIMEOUT (nvme_io_timeout * HZ) > > @@ -454,7 +455,9 @@ static inline void nvme_mpath_clear_current_path(struct nvme_ns *ns) > > { > > struct nvme_ns_head *head = ns->head; > > > > - if (head && ns == srcu_dereference(head->current_path, &head->srcu)) > > + if (head && > > + ns == rcu_dereference_protected(head->current_path, > > + lockdep_is_held(&ns->ctrl->subsys->lock))) > > rcu_assign_pointer(head->current_path, NULL); > > } > > struct nvme_ns *nvme_find_path(struct nvme_ns_head *head); > > We don't really dereference it at all in fact, but just check the > pointers for equality. I wonder if there is a better way to do this, > as my ANA patches add a caller without the lock (and withou SRU > protection either now that I think of it) - for a pure pointer compare > we really should not need any sort of protection. Uff maybe, but are you sure a comparison of two pointer is always atomic (on all architectures)? Paul, can you shed some light on us mere mortal, whether the above rcu_dereference_protected() is needed or if a simple ns == head->current_path is sufficient. Thanks, Johannes -- Johannes Thumshirn Storage jthumshirn@suse.de +49 911 74053 689 SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: Felix Imendörffer, Jane Smithard, Graham Norton HRB 21284 (AG Nürnberg) Key fingerprint = EC38 9CAB C2C4 F25D 8600 D0D0 0393 969D 2D76 0850