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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 B5820CA9EC0 for ; Tue, 29 Oct 2019 03:34:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8CC8F20873 for ; Tue, 29 Oct 2019 03:34:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726411AbfJ2Der (ORCPT ); Mon, 28 Oct 2019 23:34:47 -0400 Received: from szxga05-in.huawei.com ([45.249.212.191]:5216 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726025AbfJ2Der (ORCPT ); Mon, 28 Oct 2019 23:34:47 -0400 Received: from DGGEMS412-HUB.china.huawei.com (unknown [172.30.72.58]) by Forcepoint Email with ESMTP id 875B859B04CB6891E704; Tue, 29 Oct 2019 11:34:42 +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; Tue, 29 Oct 2019 11:34:34 +0800 Subject: Re: [PATCH] pci: lock the pci_cfg_wait queue for the consistency of data To: Matthew Wilcox CC: , , , , , , , , , , References: <20191028091809.35212-1-zhengxiang9@huawei.com> <20191028163041.GA8257@bombadil.infradead.org> From: Xiang Zheng Message-ID: <14e7d02e-215d-30dc-548c-e605f3ffdf1e@huawei.com> Date: Tue, 29 Oct 2019 11:34:33 +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: <20191028163041.GA8257@bombadil.infradead.org> 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-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org 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