From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752484AbeEOHlP (ORCPT ); Tue, 15 May 2018 03:41:15 -0400 Received: from mx2.suse.de ([195.135.220.15]:42961 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752089AbeEOHkv (ORCPT ); Tue, 15 May 2018 03:40:51 -0400 From: Johannes Thumshirn To: Keith Busch Cc: Sagi Grimberg , Christoph Hellwig , Linux NVMe Mailinglist , Linux Kernel Mailinglist , Hannes Reinecke , Johannes Thumshirn Subject: [PATCHv2 1/5] nvme: fix lockdep warning in nvme_mpath_clear_current_path Date: Tue, 15 May 2018 09:40:39 +0200 Message-Id: <20180515074043.22843-2-jthumshirn@suse.de> X-Mailer: git-send-email 2.16.3 In-Reply-To: <20180515074043.22843-1-jthumshirn@suse.de> References: <20180515074043.22843-1-jthumshirn@suse.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When running blktest's nvme/005 with a lockdep enabled kernel the test case fails due to the following lockdep splat in dmesg: [ 18.206166] ============================= [ 18.207286] WARNING: suspicious RCU usage [ 18.208417] 4.17.0-rc5 #881 Not tainted [ 18.209487] ----------------------------- [ 18.210612] drivers/nvme/host/nvme.h:457 suspicious rcu_dereference_check() usage! [ 18.213486] [ 18.213486] other info that might help us debug this: [ 18.213486] [ 18.214745] [ 18.214745] rcu_scheduler_active = 2, debug_locks = 1 [ 18.215798] 3 locks held by kworker/u32:5/1102: [ 18.216535] #0: (ptrval) ((wq_completion)"nvme-wq"){+.+.}, at: process_one_work+0x152/0x5c0 [ 18.217983] #1: (ptrval) ((work_completion)(&ctrl->scan_work)){+.+.}, at: process_one_work+0x152/0x5c0 [ 18.219584] #2: (ptrval) (&subsys->lock#2){+.+.}, at: nvme_ns_remove+0x43/0x1c0 [nvme_core] [ 18.221037] [ 18.221037] stack backtrace: [ 18.221721] CPU: 12 PID: 1102 Comm: kworker/u32:5 Not tainted 4.17.0-rc5 #881 [ 18.222830] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.0.0-prebuilt.qemu-project.org 04/01/2014 [ 18.224451] Workqueue: nvme-wq nvme_scan_work [nvme_core] [ 18.225308] Call Trace: [ 18.225704] dump_stack+0x78/0xb3 [ 18.226224] nvme_ns_remove+0x1a3/0x1c0 [nvme_core] [ 18.226975] nvme_validate_ns+0x87/0x850 [nvme_core] [ 18.227749] ? blk_queue_exit+0x69/0x110 [ 18.228358] ? blk_queue_exit+0x81/0x110 [ 18.228960] ? direct_make_request+0x1a0/0x1a0 [ 18.229649] nvme_scan_work+0x212/0x2d0 [nvme_core] [ 18.230411] process_one_work+0x1d8/0x5c0 [ 18.231037] ? process_one_work+0x152/0x5c0 [ 18.231705] worker_thread+0x45/0x3e0 [ 18.232282] kthread+0x101/0x140 [ 18.232788] ? process_one_work+0x5c0/0x5c0 The only caller of nvme_mpath_clear_current_path() is nvme_ns_remove() which holds the subsys lock so it's likely a false positive, but when using rcu_access_pointer(), we're telling rcu and lockdep that we're only after the pointer falue. Fixes: 32acab3181c7 ("nvme: implement multipath access to nvme subsystems") Signed-off-by: Johannes Thumshirn Suggested-by: Paul E. McKenney --- Changes to v1: - Change rcu_dereference_protected() to rc_access_pointer() (Paul) --- drivers/nvme/host/nvme.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h index 17d2f7cf3fed..af2bb6bc984d 100644 --- a/drivers/nvme/host/nvme.h +++ b/drivers/nvme/host/nvme.h @@ -22,6 +22,7 @@ #include #include #include +#include extern unsigned int nvme_io_timeout; #define NVME_IO_TIMEOUT (nvme_io_timeout * HZ) @@ -454,7 +455,7 @@ 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_access_pointer(head->current_path)) rcu_assign_pointer(head->current_path, NULL); } struct nvme_ns *nvme_find_path(struct nvme_ns_head *head); -- 2.16.3