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

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Message-ID: <871rpp3ba8.fsf@vitty.brq.redhat.com>
Date:   Wed, 18 Mar 2020 16:58:23 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     ltykernel@...il.com
Cc:     Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        liuwe@...rosoft.com, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, hpa@...or.com, x86@...nel.org,
        michael.h.kelley@...rosoft.com
Subject: Re: [PATCH 0/4] x86/Hyper-V: Unload vmbus channel in hv panic callback

ltykernel@...il.com writes:

> From: Tianyu Lan <Tianyu.Lan@...rosoft.com>
>
> Customer reported Hyper-V VM still responded network traffic
> ack packets after kernel panic with kernel parameter "panic=0”.
> 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@...rosoft.com>
> ---
>  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;

?

>  	/* 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);

-- 
Vitaly