Michael Kelley <mikelley@xxxxxxxxxxxxx> writes:
> vmbus_wait_for_unload() looks for a CHANNELMSG_UNLOAD_RESPONSE message
> coming from Hyper-V. But if the message isn't found for some reason,
> the panic path gets hung forever. Add a timeout of 10 seconds to prevent
> this.
If I remember correctly, the problem I was observing back then was that
if CHANNELMSG_UNLOAD_RESPONSE is not delivered, Hyper-V won't respond to
the consequent CHANNELMSG_INITIATE_CONTACT/CHANNELMSG_REQUESTOFFERS
(don't remember exactly) so we either hang here or crash in the kdump
kernel because we can't find any devices. Maybe the problem was only
with some ancient Hyper-V versions or it was fixed.
>
> Fixes: 415719160de3 ("Drivers: hv: vmbus: avoid scheduling in interrupt context in vmbus_initiate_unload()")
> Signed-off-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
> ---
> drivers/hv/channel_mgmt.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
> index 591106c..1d44bb6 100644
> --- a/drivers/hv/channel_mgmt.c
> +++ b/drivers/hv/channel_mgmt.c
> @@ -731,7 +731,7 @@ static void vmbus_wait_for_unload(void)
> void *page_addr;
> struct hv_message *msg;
> struct vmbus_channel_message_header *hdr;
> - u32 message_type;
> + u32 message_type, i;
>
> /*
> * CHANNELMSG_UNLOAD_RESPONSE is always delivered to the CPU which was
> @@ -741,8 +741,11 @@ static void vmbus_wait_for_unload(void)
> * functional and vmbus_unload_response() will complete
> * vmbus_connection.unload_event. If not, the last thing we can do is
> * read message pages for all CPUs directly.
> + *
> + * Wait no more than 10 seconds so that the panic path can't get
> + * hung forever in case the response message isn't seen.
> */
> - while (1) {
> + for (i = 0; i < 1000; i++) {
> if (completion_done(&vmbus_connection.unload_event))
> break;
LGTM,
Reviewed-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
--
Vitaly
