On 9/8/2026 5:00 PM, Sahil Chandna wrote:
A guest can wait indefinitely in wait_for_response() for the host to send either a rescind message or a packet completion. If the host does not send either, the guest can remain blocked with no diagnostic indicating a reason. This was observed during a guest kernel upgrade in which the host-side application handling the PCI channel faulted, causing the guest to never receive the completion request. Add a warning in wait_for_response() when the wait exceeds a timeout so that such a hang is visible in the guest's kernel log and can be correlated with host-side state. Suggested-by: Michael Kelley <[email protected]> Signed-off-by: Sahil Chandna <[email protected]> --- Changes since v2: - Add counter based timeout instead of introducing another timer Link to v2: https://lore.kernel.org/all/[email protected]/ Changes since v1: - Removed periodic warning to one time warning in 2 minutes - Include vmbus relid and stuck PCI msg. Link to v1: https://lore.kernel.org/all/[email protected]/ drivers/pci/controller/pci-hyperv.c | 46 ++++++++++++++++++++++------- 1 file changed, 36 insertions(+), 10 deletions(-) diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c index 89816a2bd7cd..bd07402c47ed 100644 --- a/drivers/pci/controller/pci-hyperv.c +++ b/drivers/pci/controller/pci-hyperv.c @@ -1040,19 +1040,38 @@ static void put_pcichild(struct hv_pci_dev *hpdev) /* * There is no good way to get notified from vmbus_onoffer_rescind(), - * so let's use polling here, since this is not a hot path. + * so let's use polling here, since this is not a hot path. If + * wait_for_response() has been polling for 2 minutes + * without either a rescind or completion, add a warning. */ +#define PCI_RESPONSE_HANG_TICKS 1200 +
Nit, I think this variable name could be misleading, as this represents a loop counter for a retry logic, but not exactly *ticks* from kernel terminology.
I would have preferred something like: PCI_RESPONSE_WARN_POLL_COUNT. Rest LGTM. Reviewed-by: Naman Jain <[email protected]> Regards, Naman Jain
