Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756327AbbEVH43 (ORCPT ); Fri, 22 May 2015 03:56:29 -0400 Received: from [119.145.14.65] ([119.145.14.65]:27679 "EHLO szxga02-in.huawei.com" rhost-flags-FAIL-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1751783AbbEVH4W (ORCPT ); Fri, 22 May 2015 03:56:22 -0400 Message-ID: <555EE0F2.1010109@huawei.com> Date: Fri, 22 May 2015 15:55:30 +0800 From: Yijing Wang User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:24.0) Gecko/20100101 Thunderbird/24.0.1 MIME-Version: 1.0 To: Bjorn Helgaas , Yinghai Lu , "Jeff Kirsher" CC: , , , Subject: Re: e1000e pci_disable_link_state_locked() issues References: <20150520194749.GA10210@google.com> In-Reply-To: <20150520194749.GA10210@google.com> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.177.27.212] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2881 Lines: 68 On 2015/5/21 3:47, Bjorn Helgaas wrote: > I think we have some issues with the e1000e usage of > pci_disable_link_state_locked(), which Yinghai added with 9f728f53dd70 > ("PCI/e1000e: Add and use pci_disable_link_state_locked()"). > > That fixed an AER deadlock in the following path, where pci_bus_sem is held > by pci_walk_bus(), and we deadlocked when we tried to re-acquire it in > pci_disable_link_state(): > > do_recovery > broadcast_error_message(..., report_slot_reset) > pci_walk_bus > down_read(&pci_bus_sem) > cb(...) # report_slot_reset > report_slot_reset > dev->driver->err_handler->slot_reset # e1000_io_slot_reset > e1000_io_slot_reset > e1000e_disable_aspm > pci_disable_link_state > down_read(&pci_bus_sem) > > 9f728f53dd70 fixed that by changing e1000e_disable_aspm() to use > pci_disable_link_state_locked() instead, which assumes pci_bus_sem is > already held. > > That's fine for the e1000_io_slot_reset() path, where pci_bus_sem really > *is* held. But e1000e_disable_aspm() is also called from e1000_probe() and > __e1000_resume(), and in those paths, we *don't* hold pci_bus_sem. > > In effect, the caller of pci_disable_link_state_locked() is promising that > pci_bus_sem is held, and __pci_disable_link_state() relies on that promise > for its locking. But e1000e isn't upholding its end of the bargain. > > I'm not 100% sure __pci_disable_link_state() actually *needs* that locking: > it is only called from a driver, and it should be impossible for a device > or any upstream bridge to go away while a driver is bound to it. If Another question, when pci_disable_link_state() is called in driver, the device and its upstream bridge do not go away while a driver is bound to it, but what about a new function device adding to the upstream bridge secondary bus. In this case, traverse the pci_bus->devices list may be not safe. > somebody wanted to analyze this further and propose a patch to remove the > locking (if it seems safe), that would be great. > > But in any case, __pci_disable_link_state() should be able to rely on its > callers following the rules, so I'd like to see an e1000e change to use > pci_disable_link_state() from the paths where pci_bus_sem is not held. > > Bjorn > -- > To unsubscribe from this list: send the line "unsubscribe linux-pci" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > > -- Thanks! Yijing -- 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/