From: Dexuan Cui decui@microsoft.com Sent: Monday, April 3, 2023 7:06 PM

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@microsoft.com Cc: stable@vger.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• * 'comp' is no longer valid.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

Reviewed-by: Michael Kelley mikelley@microsoft.com