From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga09.intel.com ([134.134.136.24]:60458 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751981AbeCUQA0 (ORCPT ); Wed, 21 Mar 2018 12:00:26 -0400 Date: Wed, 21 Mar 2018 10:02:39 -0600 From: Keith Busch To: Ming Lei Cc: Marta Rybczynska , axboe@fb.com, hch@lst.de, sagi@grimberg.me, linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org, bhelgaas@google.com, linux-pci@vger.kernel.org, Pierre-Yves Kerbrat Subject: Re: [RFC PATCH] nvme: avoid race-conditions when enabling devices Message-ID: <20180321160238.GF12909@localhost.localdomain> References: <744877924.5841545.1521630049567.JavaMail.zimbra@kalray.eu> <20180321115037.GA26083@ming.t460p> <464125757.5843583.1521634231341.JavaMail.zimbra@kalray.eu> <20180321154807.GD22254@ming.t460p> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20180321154807.GD22254@ming.t460p> Sender: linux-pci-owner@vger.kernel.org List-ID: On Wed, Mar 21, 2018 at 11:48:09PM +0800, Ming Lei wrote: > On Wed, Mar 21, 2018 at 01:10:31PM +0100, Marta Rybczynska wrote: > > > On Wed, Mar 21, 2018 at 12:00:49PM +0100, Marta Rybczynska wrote: > > >> NVMe driver uses threads for the work at device reset, including enabling > > >> the PCIe device. When multiple NVMe devices are initialized, their reset > > >> works may be scheduled in parallel. Then pci_enable_device_mem can be > > >> called in parallel on multiple cores. > > >> > > >> This causes a loop of enabling of all upstream bridges in > > >> pci_enable_bridge(). pci_enable_bridge() causes multiple operations > > >> including __pci_set_master and architecture-specific functions that > > >> call ones like and pci_enable_resources(). Both __pci_set_master() > > >> and pci_enable_resources() read PCI_COMMAND field in the PCIe space > > >> and change it. This is done as read/modify/write. > > >> > > >> Imagine that the PCIe tree looks like: > > >> A - B - switch - C - D > > >> \- E - F > > >> > > >> D and F are two NVMe disks and all devices from B are not enabled and bus > > >> mastering is not set. If their reset work are scheduled in parallel the two > > >> modifications of PCI_COMMAND may happen in parallel without locking and the > > >> system may end up with the part of PCIe tree not enabled. > > > > > > Then looks serialized reset should be used, and I did see the commit > > > 79c48ccf2fe ("nvme-pci: serialize pci resets") fixes issue of 'failed > > > to mark controller state' in reset stress test. > > > > > > But that commit only covers case of PCI reset from sysfs attribute, and > > > maybe other cases need to be dealt with in similar way too. > > > > > > > It seems to me that the serialized reset works for multiple resets of the > > same device, doesn't it? Our problem is linked to resets of different devices > > that share the same PCIe tree. > > Given reset shouldn't be a frequent action, it might be fine to serialize all > reset from different devices. The driver was much simpler when we had serialized resets in line with probe, but that had a bigger problems with certain init systems when you put enough nvme devices in your server, making them unbootable. Would it be okay to serialize just the pci_enable_device across all other tasks messing with the PCI topology? --- diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c index cef5ce851a92..e0a2f6c0f1cf 100644 --- a/drivers/nvme/host/pci.c +++ b/drivers/nvme/host/pci.c @@ -2094,8 +2094,11 @@ static int nvme_pci_enable(struct nvme_dev *dev) int result = -ENOMEM; struct pci_dev *pdev = to_pci_dev(dev->dev); - if (pci_enable_device_mem(pdev)) - return result; + pci_lock_rescan_remove(); + result = pci_enable_device_mem(pdev); + pci_unlock_rescan_remove(); + if (result) + return -ENODEV; pci_set_master(pdev); --