Re: [PATCH 0/4] x86/Hyper-V: Unload vmbus channel in hv panic callback

[Tianyu Lan]

Hi Vitaly:
     Thanks for your review.

On 3/18/2020 11:58 PM, Vitaly Kuznetsov wrote:
> ltykernel@xxxxxxxxx writes:
>
> > From: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx>
> >
> > Customer reported Hyper-V VM still responded network traffic
> > ack packets after kernel panic with kernel parameter "panic=0â.
> > This becauses vmbus driver interrupt handler still works
> > on the panic cpu after kernel panic. Panic cpu falls into
> > infinite loop of panic() with interrupt enabled at that point.
> > Vmbus driver can still handle network traffic.
> >
> > This confuses remote service that the panic system is still
> > alive when it gets ack packets. Unload vmbus channel in hv panic
> > callback and fix it.
> >
> > vmbus_initiate_unload() maybe double called during panic process
> > (e.g, hyperv_panic_event() and hv_crash_handler()). So check
> > and set connection state in vmbus_initiate_unload() to resolve
> > reenter issue.
> >
> > Signed-off-by: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx>
> > ---
> >   drivers/hv/channel_mgmt.c |  5 +++++
> >   drivers/hv/vmbus_drv.c    | 17 +++++++++--------
> >   2 files changed, 14 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
> > index 0370364169c4..893493f2b420 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 (vmbus_connection.conn_state == DISCONNECTED)
> > +		return;
> > +
>
> To make this less racy, can we do something like
>
> 	if (xchg(&vmbus_connection.conn_state, DISCONNECTED) == DISCONNECTED)
> 		return;
>
> ?

Agree. Will update in the next version.

> >   	/* Pre-Win2012R2 hosts don't support reconnect */
> >   	if (vmbus_proto_version < VERSION_WIN8_1)
> >   		return;
> > @@ -857,6 +860,8 @@ void vmbus_initiate_unload(bool crash)
> >   		wait_for_completion(&vmbus_connection.unload_event);
> >   	else
> >   		vmbus_wait_for_unload();
> > +
> > +	vmbus_connection.conn_state = DISCONNECTED;
> >   }
> >   
> >   static void check_ready_for_resume_event(void)
> > 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) {
>
> With Michael's effors to make code in drivers/hv arch agnostic, I think
> we need a better, arch-neutral way.
>
> > +		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.*/
> > +	atomic_notifier_chain_register(&panic_notifier_list,
> > +			       &hyperv_panic_block);
> > +
> >   	vmbus_request_offers();
> >   
> >   	return 0;
> > @@ -2204,8 +2209,6 @@ static int vmbus_bus_suspend(struct device *dev)
> >   
> >   	vmbus_initiate_unload(false);
> >   
> > -	vmbus_connection.conn_state = DISCONNECTED;
> > -
> >   	/* Reset the event for the next resume. */
> >   	reinit_completion(&vmbus_connection.ready_for_resume_event);
> >   
> > @@ -2289,7 +2292,6 @@ static void hv_kexec_handler(void)
> >   {
> >   	hv_stimer_global_cleanup();
> >   	vmbus_initiate_unload(false);
> > -	vmbus_connection.conn_state = DISCONNECTED;
> >   	/* Make sure conn_state is set as hv_synic_cleanup checks for it */
> >   	mb();
> >   	cpuhp_remove_state(hyperv_cpuhp_online);
> > @@ -2306,7 +2308,6 @@ static void hv_crash_handler(struct pt_regs *regs)
> >   	 * doing the cleanup for current CPU only. This should be sufficient
> >   	 * for kdump.
> >   	 */
> > -	vmbus_connection.conn_state = DISCONNECTED;
> >   	cpu = smp_processor_id();
> >   	hv_stimer_cleanup(cpu);
> >   	hv_synic_disable_regs(cpu);