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 periodic 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: Hamza Mahfooz <[email protected]> Signed-off-by: Sahil Chandna <[email protected]> --- This was sent earlier upstream [1] [1] https://lore.kernel.org/linux-hyperv/[email protected]/ --- drivers/pci/controller/pci-hyperv.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c index cfc8fa403dad..c4fba0039164 100644 --- a/drivers/pci/controller/pci-hyperv.c +++ b/drivers/pci/controller/pci-hyperv.c @@ -1040,11 +1040,18 @@ 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 PCI_RESPONSE_HANG_TIMEOUT_SEC + * without either a rescind or completion, add a periodic warning. */ +#define PCI_RESPONSE_HANG_TIMEOUT_SEC 300 + static int wait_for_response(struct hv_device *hdev, struct completion *comp) { + unsigned long delay = secs_to_jiffies(PCI_RESPONSE_HANG_TIMEOUT_SEC); + u64 timeout = get_jiffies_64() + delay; + while (true) { if (hdev->channel->rescind) { dev_warn_once(&hdev->device, "The device is gone.\n"); @@ -1053,6 +1060,11 @@ static int wait_for_response(struct hv_device *hdev, if (wait_for_completion_timeout(comp, HZ / 10)) break; + + if (time_after64(get_jiffies_64(), timeout)) { + dev_warn(&hdev->device, "PCI stuck waiting for response.\n"); + timeout = get_jiffies_64() + delay; + } } return 0; -- 2.53.0
