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Tue, 28 Mar 2023 04:53:06 +0000 From: Dexuan Cui To: bhelgaas@google.com, davem@davemloft.net, decui@microsoft.com, edumazet@google.com, haiyangz@microsoft.com, jakeo@microsoft.com, kuba@kernel.org, kw@linux.com, kys@microsoft.com, leon@kernel.org, linux-pci@vger.kernel.org, lpieralisi@kernel.org, mikelley@microsoft.com, pabeni@redhat.com, robh@kernel.org, saeedm@nvidia.com, wei.liu@kernel.org, longli@microsoft.com, boqun.feng@gmail.com Cc: linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org, linux-rdma@vger.kernel.org, netdev@vger.kernel.org Subject: [PATCH 1/6] PCI: hv: fix a race condition bug in hv_pci_query_relations() Date: Mon, 27 Mar 2023 21:51:17 -0700 Message-Id: <20230328045122.25850-2-decui@microsoft.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20230328045122.25850-1-decui@microsoft.com> References: <20230328045122.25850-1-decui@microsoft.com> X-ClientProxiedBy: MW4PR03CA0013.namprd03.prod.outlook.com (2603:10b6:303:8f::18) To BL0PR2101MB1092.namprd21.prod.outlook.com (2603:10b6:207:30::23) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BL0PR2101MB1092:EE_|IA1PR21MB3402:EE_ X-MS-Office365-Filtering-Correlation-Id: 585f1308-72af-4103-5705-08db2f48522a X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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Fixes: 4daace0d8ce8 ("PCI: hv: Add paravirtual PCI front-end for Microsoft Hyper-V VMs") Signed-off-by: Dexuan Cui --- drivers/pci/controller/pci-hyperv.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) With the below debug code: @@ -2103,6 +2103,8 @@ static void survey_child_resources(struct hv_pcibus_device *hbus) } spin_unlock_irqrestore(&hbus->device_list_lock, flags); + ssleep(15); + printk("%s: completing %px\n", __func__, event); complete(event); } @@ -3305,8 +3307,12 @@ static int hv_pci_query_relations(struct hv_device *hdev) ret = vmbus_sendpacket(hdev->channel, &message, sizeof(message), 0, VM_PKT_DATA_INBAND, 0); - if (!ret) + if (!ret) { + ssleep(10); // unassign the PCI device on the host during the 10s ret = wait_for_response(hdev, &comp); + printk("%s: comp=%px is becoming invalid! ret=%d\n", + __func__, &comp, ret); + } return ret; } @@ -3635,6 +3641,8 @@ static int hv_pci_probe(struct hv_device *hdev, retry: ret = hv_pci_query_relations(hdev); + printk("hv_pci_query_relations() exited\n"); + if (ret) goto free_irq_domain; I'm able to repro the below hang issue: [ 74.544744] hv_pci b92a0085-468b-407a-a88a-d33fac8edc75: PCI VMBus probing: Using version 0x10004 [ 76.886944] hv_netvsc 818fe754-b912-4445-af51-1f584812e3c9 eth0: VF slot 1 removed [ 84.788266] hv_pci b92a0085-468b-407a-a88a-d33fac8edc75: The device is gone. [ 84.792586] hv_pci_query_relations: comp=ffffa7504012fb58 is becoming invalid! ret=-19 [ 84.797505] hv_pci_query_relations() exited [ 89.652268] survey_child_resources: completing ffffa7504012fb58 [ 150.392242] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: [ 150.398447] rcu: 15-...0: (2 ticks this GP) idle=867c/1/0x4000000000000000 softirq=947/947 fqs=5234 [ 150.405851] rcu: (detected by 14, t=15004 jiffies, g=2553, q=4833 ncpus=16) [ 150.410870] Sending NMI from CPU 14 to CPUs 15: [ 150.414836] NMI backtrace for cpu 15 [ 150.414840] CPU: 15 PID: 10 Comm: kworker/u32:0 Tainted: G W E 6.3.0-rc3-decui-dirty #34 ... [ 150.414849] Workqueue: hv_pci_468b pci_devices_present_work [pci_hyperv] [ 150.414866] RIP: 0010:__pv_queued_spin_lock_slowpath+0x10f/0x3c0 ... [ 150.414905] Call Trace: [ 150.414907] [ 150.414911] _raw_spin_lock_irqsave+0x40/0x50 [ 150.414917] complete+0x1d/0x60 [ 150.414924] pci_devices_present_work+0x5dd/0x680 [pci_hyperv] [ 150.414946] process_one_work+0x21f/0x430 [ 150.414952] worker_thread+0x4a/0x3c0 With this patch, the hang issue goes away: [ 186.143612] hv_pci b92a0085-468b-407a-a88a-d33fac8edc75: The device is gone. [ 186.148034] hv_pci_query_relations: comp=ffffa7cfd0aa3b50 is becoming invalid! ret=-19 [ 191.263611] survey_child_resources: completing ffffa7cfd0aa3b50 [ 191.267732] hv_pci_query_relations() exited diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c index f33370b75628..b82c7cde19e6 100644 --- a/drivers/pci/controller/pci-hyperv.c +++ b/drivers/pci/controller/pci-hyperv.c @@ -3308,6 +3308,19 @@ static int hv_pci_query_relations(struct hv_device *hdev) if (!ret) ret = wait_for_response(hdev, &comp); + /* + * In the case of fast device addition/removal, it's possible that + * vmbus_sendpacket() or wait_for_response() returns -ENODEV but we + * already got a PCI_BUS_RELATIONS* message from the host and the + * channel callback already scheduled a work to hbus->wq, which can be + * running survey_child_resources() -> complete(&hbus->survey_event), + * even after hv_pci_query_relations() exits and the stack variable + * 'comp' is no longer valid. This can cause a strange hang issue + * or sometimes a page fault. Flush hbus->wq before we exit from + * hv_pci_query_relations() to avoid the issues. + */ + flush_workqueue(hbus->wq); + return ret; }