From: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx> Sent: Monday, March 23, 2020 6:09 AM
>
> When kdump is not configured, a Hyper-V VM might still respond to
> network traffic after a kernel panic when kernel parameter panic=0.
> The panic CPU goes into an infinite loop with interrupts enabled,
> and the VMbus driver interrupt handler still works because the
> VMbus connection is unloaded only in the kdump path. The network
> responses make the other end of the connection think the VM is
> still functional even though it has panic'ed, which could affect any
> failover actions that should be taken.
>
> Fix this by unloading the VMbus connection during the panic process.
> vmbus_initiate_unload() could then be called twice (e.g., by
> hyperv_panic_event() and hv_crash_handler(), so reset the connection
> state in vmbus_initiate_unload() to ensure the unload is done only
> once.
>
> Signed-off-by: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx>
> ---
> Change since v1:
> - Update chnage log
> - Use xchg() to change vmbus connection status
> ---
> drivers/hv/channel_mgmt.c | 3 +++
> drivers/hv/vmbus_drv.c | 17 +++++++++--------
> 2 files changed, 12 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
> index 0370364169c4..501c43c5851d 100644
> --- a/drivers/hv/channel_mgmt.c
> +++ b/drivers/hv/channel_mgmt.c
> @@ -839,6 +839,9 @@ void vmbus_initiate_unload(bool crash)
> {
> struct vmbus_channel_message_header hdr;
>
> + if (xchg(&vmbus_connection.conn_state, DISCONNECTED) == DISCONNECTED)
> + return;
> +
> /* Pre-Win2012R2 hosts don't support reconnect */
> if (vmbus_proto_version < VERSION_WIN8_1)
> return;
> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> index 029378c27421..b56b9fb9bd90 100644
> --- a/drivers/hv/vmbus_drv.c
> +++ b/drivers/hv/vmbus_drv.c
> @@ -53,9 +53,12 @@ static int hyperv_panic_event(struct notifier_block *nb, unsigned
> long val,
> {
> struct pt_regs *regs;
>
> - regs = current_pt_regs();
> + vmbus_initiate_unload(true);
>
> - hyperv_report_panic(regs, val);
> + if (ms_hyperv.misc_features & HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE) {
> + regs = current_pt_regs();
> + hyperv_report_panic(regs, val);
> + }
> return NOTIFY_DONE;
> }
>
> @@ -1391,10 +1394,12 @@ static int vmbus_bus_init(void)
> }
>
> register_die_notifier(&hyperv_die_block);
> - atomic_notifier_chain_register(&panic_notifier_list,
> - &hyperv_panic_block);
> }
>
> + /* Vmbus channel is unloaded in panic callback when panic happens.*/
Let me suggest a tweak to the above comment so it is super clear:
/*
* Always register the panic notifier because we need to unload
* the VMbus channel connection to prevent any VMbus
* activity after the VM panics.
*/
> + atomic_notifier_chain_register(&panic_notifier_list,
> + &hyperv_panic_block);
> +
> vmbus_request_offers();
>
> return 0;
