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@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
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+ * 'comp' is no longer valid.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
