netdev - [PATCH v2 1/6] PCI: hv: Fix a race condition bug in hv_pci_query

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Message-Id: <20230404020545.32359-2-decui@microsoft.com>
Date:   Mon,  3 Apr 2023 19:05:40 -0700
From:   Dexuan Cui <decui@...rosoft.com>
To:     bhelgaas@...gle.com, davem@...emloft.net, decui@...rosoft.com,
        edumazet@...gle.com, haiyangz@...rosoft.com, jakeo@...rosoft.com,
        kuba@...nel.org, kw@...ux.com, kys@...rosoft.com, leon@...nel.org,
        linux-pci@...r.kernel.org, lpieralisi@...nel.org,
        mikelley@...rosoft.com, pabeni@...hat.com, robh@...nel.org,
        saeedm@...dia.com, wei.liu@...nel.org, longli@...rosoft.com,
        boqun.feng@...il.com, ssengar@...rosoft.com, helgaas@...nel.org
Cc:     linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-rdma@...r.kernel.org, netdev@...r.kernel.org,
        stable@...r.kernel.org
Subject: [PATCH v2 1/6] PCI: hv: Fix a race condition bug in hv_pci_query_relations()

Fix the longstanding race between hv_pci_query_relations() and
survey_child_resources() 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 <decui@...rosoft.com>
Cc: stable@...r.kernel.org
---

v2: 
  Removed the "debug code".
  No change to the patch body.
  Added Cc:stable

 drivers/pci/controller/pci-hyperv.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
index f33370b756283..b82c7cde19e66 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+	 * 'comp' is no longer valid.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;
 }
 
-- 
2.25.1