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

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commit 440b5e3663271b0ffbd4908115044a6a51fb938b upstream.

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device-remove and the stack variable 'comp' is no longer valid;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: 4daace0d8c ("PCI: hv: Add paravirtual PCI front-end for Microsoft Hyper-V VMs")
Signed-off-by: Dexuan Cui <decui@microsoft.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Acked-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20230615044451.5580-2-decui@microsoft.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Dexuan Cui 2023-06-14 21:44:47 -07:00 committed by Greg Kroah-Hartman
parent 8b8c9812c0
commit 79ceb758e3
1 changed files with 18 additions and 0 deletions
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18
drivers/pci/controller/pci-hyperv.c
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@ -2912,6 +2912,24 @@ 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* exits and the stack variable 'comp' is no longer valid; as a result,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;
}