Commit 440b5e36 authored by Dexuan Cui's avatar Dexuan Cui Committed by Wei Liu
Browse files

PCI: hv: Fix a race condition bug in hv_pci_query_relations() 



Since day 1 of the driver, there has been a race between
hv_pci_query_relations() and survey_child_resources(): during fast
device hotplug, hv_pci_query_relations() may error out due to
device-remove and the stack variable 'comp' is no longer valid;
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: 4daace0d ("PCI: hv: Add paravirtual PCI front-end for Microsoft Hyper-V VMs")
Signed-off-by: default avatarDexuan Cui <decui@microsoft.com>
Reviewed-by: default avatarMichael Kelley <mikelley@microsoft.com>
Acked-by: default avatarLorenzo Pieralisi <lpieralisi@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20230615044451.5580-2-decui@microsoft.com


Signed-off-by: default avatarWei Liu <wei.liu@kernel.org>
parent 52ae076c

drivers/pci/controller/pci-hyperv.c

+18 −0
Original line number Diff line number Diff line
@@ -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	 * exits and the stack variable 'comp' is no longer valid; as a result,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;

}