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

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Date:   Tue, 17 Mar 2020 17:35:53 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     ltykernel@...il.com
Cc:     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,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        vkuznets@...hat.com, Wei Liu <wei.liu@...nel.org>
Subject: Re: [PATCH 0/4] x86/Hyper-V: Unload vmbus channel in hv panic
 callback

On Tue, Mar 17, 2020 at 06:25:20AM -0700, ltykernel@...il.com wrote:
> 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;
> +
>  	/* 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;

This is only set at the end of the function.  I don't see how this solve
the re-entrant issue with the check at the beginning. Do I miss anything
here?

Maybe this function should check and set the state to
DISCONNECTING/DISCONNECTED at the beginning of this function?

Wei.