[PATCH] PCI: hv: Warn when wait_for_response() waits indefinitely

[Sahil Chandna <sahilchandna@linux.microsoft.com>]

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 <hamzamahfooz@linux.microsoft.com>
Signed-off-by: Sahil Chandna <sahilchandna@linux.microsoft.com>
---
This was sent earlier upstream [1]
[1] https://lore.kernel.org/linux-hyperv/20260612174010.2598695-1-hamzamahfooz@linux.microsoft.com/
---
 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