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Thu, 15 Jun 2023 04:45:37 +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, ssengar@microsoft.com, helgaas@kernel.org Cc: linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org, linux-rdma@vger.kernel.org, netdev@vger.kernel.org, josete@microsoft.com, simon.horman@corigine.com, stable@vger.kernel.org Subject: [PATCH v4 1/5] PCI: hv: Fix a race condition bug in hv_pci_query_relations() Date: Wed, 14 Jun 2023 21:44:47 -0700 Message-Id: <20230615044451.5580-2-decui@microsoft.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20230615044451.5580-1-decui@microsoft.com> References: <20230615044451.5580-1-decui@microsoft.com> X-ClientProxiedBy: CYZPR17CA0016.namprd17.prod.outlook.com (2603:10b6:930:8c::25) 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_|PH7PR21MB3382:EE_ X-MS-Office365-Filtering-Correlation-Id: e72a2ae8-3426-4843-736f-08db6d5b5ce3 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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however, pci_devices_present_work() -> survey_child_resources() -> complete() may be running on another CPU and accessing the no-longer-valid 'comp'. Fix the race by flushing the workqueue before we exit from hv_pci_query_relations(). Fixes: 4daace0d8ce8 ("PCI: hv: Add paravirtual PCI front-end for Microsoft Hyper-V VMs") Signed-off-by: Dexuan Cui Reviewed-by: Michael Kelley Acked-by: Lorenzo Pieralisi Cc: stable@vger.kernel.org --- v2: Removed the "debug code". No change to the patch body. Added Cc:stable v3: Added Michael's Reviewed-by. v4: Provided more details of the issue in the comment and commit log. Added Lorenzo's Acked-by. drivers/pci/controller/pci-hyperv.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c index bc32662c6bb7f..ea8862e656b68 100644 --- a/drivers/pci/controller/pci-hyperv.c +++ b/drivers/pci/controller/pci-hyperv.c @@ -3401,6 +3401,24 @@ 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 pci_devices_present_work() -> survey_child_resources() -> + * complete(&hbus->survey_event), even after hv_pci_query_relations() + * exits and the stack variable 'comp' is no longer valid; as a result, + * a hang or a page fault may happen when the complete() calls + * raw_spin_lock_irqsave(). Flush hbus->wq before we exit from + * hv_pci_query_relations() to avoid the issues. Note: if 'ret' is + * -ENODEV, there can't be any more work item scheduled to hbus->wq + * after the flush_workqueue(): see vmbus_onoffer_rescind() -> + * vmbus_reset_channel_cb(), vmbus_rescind_cleanup() -> + * channel->rescind = true. + */ + flush_workqueue(hbus->wq); + return ret; }