On Wed, Apr 19, 2023 at 07:40:32PM -0700, Dexuan Cui wrote:
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().
"Fix the longstanding race" is vague. Please describe the race succinctly at least to give an idea of what the problem is.
Fixes: 4daace0d8ce8 ("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 Cc: stable@vger.kernel.org
v2: Removed the "debug code". No change to the patch body. Added Cc:stable
v3: Added Michael's Reviewed-by.
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survey_event),* even after hv_pci_query_relations() exits and the stack variable* 'comp' is no longer valid.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
"A strange hang" sounds like we don't understand what's happening, it does not feel like it is a solid understanding of the issue.
I would remove it - given that you already explain that comp is no longer valid - that is already a bug that needs fixing.
Acked-by: Lorenzo Pieralisi lpieralisi@kernel.org
* 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