[SRU][Xenial][PATCH 3/3] UBUNTU: SAUCE: pci-hyperv: lock pci bus on device eject

[Joseph Salisbury]

From: Long Li <longli at microsoft.com>

BugLink: http://bugs.launchpad.net/bugs/1665097

A PCI_EJECT message can arrive at the same time we are calling 
pci_scan_child_bus in the workqueue for the previous PCI_BUS_RELATIONS 
message or in create_root_hv_pci_bus(), in this case we could potentailly 
modify the bus from multiple places. Properly lock the bus access.

Thanks Dexuan Cui <decui at microsoft.com> for pointing out the race 
condition in create_root_hv_pci_bus().

Signed-off-by: Long Li <longli at microsoft.com>
Reported-by: Xiaofeng Wang <xiaofwan at redhat.com>
Signed-off-by: Joseph Salisbury <joseph.salisbury at canonical.com>
---
 drivers/pci/host/pci-hyperv.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/pci/host/pci-hyperv.c b/drivers/pci/host/pci-hyperv.c
index d4a7994..669d54d 100644
--- a/drivers/pci/host/pci-hyperv.c
+++ b/drivers/pci/host/pci-hyperv.c
@@ -1200,9 +1200,11 @@ static int create_root_hv_pci_bus(struct hv_pcibus_device *hbus)
 	hbus->pci_bus->msi = &hbus->msi_chip;
 	hbus->pci_bus->msi->dev = &hbus->hdev->device;
 
+	pci_lock_rescan_remove();
 	pci_scan_child_bus(hbus->pci_bus);
 	pci_bus_assign_resources(hbus->pci_bus);
 	pci_bus_add_devices(hbus->pci_bus);
+	pci_unlock_rescan_remove();
 	hbus->state = hv_pcibus_installed;
 	return 0;
 }
@@ -1593,8 +1595,10 @@ static void hv_eject_device_work(struct work_struct *work)
 	pdev = pci_get_domain_bus_and_slot(hpdev->hbus->sysdata.domain, 0,
 					   wslot);
 	if (pdev) {
+		pci_lock_rescan_remove();
 		pci_stop_and_remove_bus_device(pdev);
 		pci_dev_put(pdev);
+		pci_unlock_rescan_remove();
 	}
 
 	memset(&ctxt, 0, sizeof(ctxt));
-- 
2.7.4