From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 50EC4C5DF61 for ; Fri, 8 Nov 2019 01:12:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2C6962178F for ; Fri, 8 Nov 2019 01:12:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728072AbfKHBMO (ORCPT ); Thu, 7 Nov 2019 20:12:14 -0500 Received: from szxga07-in.huawei.com ([45.249.212.35]:38140 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725928AbfKHBMN (ORCPT ); Thu, 7 Nov 2019 20:12:13 -0500 Received: from DGGEMS412-HUB.china.huawei.com (unknown [172.30.72.60]) by Forcepoint Email with ESMTP id 191CBEA3289722D713FD; Fri, 8 Nov 2019 09:12:11 +0800 (CST) Received: from [127.0.0.1] (10.133.224.57) by DGGEMS412-HUB.china.huawei.com (10.3.19.212) with Microsoft SMTP Server id 14.3.439.0; Fri, 8 Nov 2019 09:12:04 +0800 Subject: Re: [PATCH] pci: lock the pci_cfg_wait queue for the consistency of data From: Xiang Zheng To: Matthew Wilcox CC: , , , , , , , , , , References: <20191028091809.35212-1-zhengxiang9@huawei.com> <20191028163041.GA8257@bombadil.infradead.org> <14e7d02e-215d-30dc-548c-e605f3ffdf1e@huawei.com> Message-ID: <5692a244-d6c7-8bd4-c7c4-e4532e7ff07c@huawei.com> Date: Fri, 8 Nov 2019 09:12:03 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:68.0) Gecko/20100101 Thunderbird/68.1.0 MIME-Version: 1.0 In-Reply-To: <14e7d02e-215d-30dc-548c-e605f3ffdf1e@huawei.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.133.224.57] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Ping... On 2019/10/29 11:34, Xiang Zheng wrote: > > > On 2019/10/29 0:30, Matthew Wilcox wrote: >> On Mon, Oct 28, 2019 at 05:18:09PM +0800, Xiang Zheng wrote: >>> Commit "7ea7e98fd8d0" suggests that the "pci_lock" is sufficient, >>> and all the callers of pci_wait_cfg() are wrapped with the "pci_lock". >>> >>> However, since the commit "cdcb33f98244" merged, the accesses to >>> the pci_cfg_wait queue are not safe anymore. A "pci_lock" is >>> insufficient and we need to hold an additional queue lock while >>> read/write the wait queue. >>> >>> So let's use the add_wait_queue()/remove_wait_queue() instead of >>> __add_wait_queue()/__remove_wait_queue(). >> >> As I said earlier, this reintroduces the deadlock addressed by >> cdcb33f9824429a926b971bf041a6cec238f91ff >> > > Thanks Matthew, sorry for that I did not understand the way to reintroduce > the deadlock and sent this patch. If what I think is right, the possible > deadlock may be caused by the condition in which there are three processes: > > *Process* *Acquired* *Wait For* > wake_up_all() wq_head->lock pi_lock > snbep_uncore_pci_read_counter() pi_lock pci_lock > pci_wait_cfg() pci_lock wq_head->lock > > These processes suffer from the nested locks.:) > > But for this problem, what do you think about the solution below: > > diff --git a/drivers/pci/access.c b/drivers/pci/access.c > index 2fccb5762c76..09342a74e5ea 100644 > --- a/drivers/pci/access.c > +++ b/drivers/pci/access.c > @@ -207,14 +207,14 @@ static noinline void pci_wait_cfg(struct pci_dev *dev) > { > DECLARE_WAITQUEUE(wait, current); > > - __add_wait_queue(&pci_cfg_wait, &wait); > do { > set_current_state(TASK_UNINTERRUPTIBLE); > raw_spin_unlock_irq(&pci_lock); > + add_wait_queue(&pci_cfg_wait, &wait); > schedule(); > + remove_wait_queue(&pci_cfg_wait, &wait); > raw_spin_lock_irq(&pci_lock); > } while (dev->block_cfg_access); > - __remove_wait_queue(&pci_cfg_wait, &wait); > } > > /* Returns 0 on success, negative values indicate error. */ > > > >> . >> > -- Thanks, Xiang