linux-kernel - RE: [PATCH] Drivers: hv: vmbus: Ignore CHANNELMSG_TL_CONNECT

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Date:   Sat, 18 Jan 2020 17:29:17 +0000
From:   Michael Kelley <mikelley@...rosoft.com>
To:     Dexuan Cui <decui@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "sashal@...nel.org" <sashal@...nel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Sasha Levin <Alexander.Levin@...rosoft.com>
CC:     Sunil Muthuswamy <sunilmut@...rosoft.com>,
        Andrea Parri <Andrea.Parri@...rosoft.com>
Subject: RE: [PATCH] Drivers: hv: vmbus: Ignore
 CHANNELMSG_TL_CONNECT_RESULT(23)

From: Dexuan Cui <decui@...rosoft.com> Sent: Thursday, January 9, 2020 5:25 PM
> 
> When a Linux hv_sock app tries to connect to a Service GUID on which no
> host app is listening, a recent host (RS3+) sends a
> CHANNELMSG_TL_CONNECT_RESULT (23) message to Linux and this triggers such
> a warning:
> 
> unknown msgtype=23
> WARNING: CPU: 2 PID: 0 at drivers/hv/vmbus_drv.c:1031 vmbus_on_msg_dpc
> 
> Actually Linux can safely ignore the message because the Linux app's
> connect() will time out in 2 seconds: see VSOCK_DEFAULT_CONNECT_TIMEOUT
> and vsock_stream_connect(). We don't bother to make use of the message
> because: 1) it's only supported on recent hosts; 2) a non-trivial effort
> is required to use the message in Linux, but the benefit is small.
> 
> So, let's not see the warning by silently ignoring the message.
> 
> Signed-off-by: Dexuan Cui <decui@...rosoft.com>
> ---
>  drivers/hv/vmbus_drv.c | 5 +++++
>  include/linux/hyperv.h | 2 ++
>  2 files changed, 7 insertions(+)
> 
> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> index 4ef5a66df680..c838b6f5f726 100644
> --- a/drivers/hv/vmbus_drv.c
> +++ b/drivers/hv/vmbus_drv.c
> @@ -1033,6 +1033,11 @@ void vmbus_on_msg_dpc(unsigned long data)
>  	}
> 
>  	entry = &channel_message_table[hdr->msgtype];
> +
> +	/* Linux ignores some messages, e.g. CHANNELMSG_TL_CONNECT_RESULT. */
> +	if (!entry->message_handler)
> +		goto msg_handled;
> +

FWIW, with this new check, all of the validity checks in vmbus_onmessage() are
redundant and could be removed.  There's already a check here that ensures
msgtype won't be too big, and this new check ensures that message_handler is
not NULL.

>  	if (entry->handler_type	== VMHT_BLOCKING) {
>  		ctx = kmalloc(sizeof(*ctx), GFP_ATOMIC);
>  		if (ctx == NULL)
> diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
> index 26f3aeeae1ca..41c58011431e 100644
> --- a/include/linux/hyperv.h
> +++ b/include/linux/hyperv.h
> @@ -425,6 +425,8 @@ enum vmbus_channel_message_type {
>  	CHANNELMSG_19				= 19,
>  	CHANNELMSG_20				= 20,
>  	CHANNELMSG_TL_CONNECT_REQUEST		= 21,
> +	CHANNELMSG_22				= 22,
> +	CHANNELMSG_TL_CONNECT_RESULT		= 23,
>  	CHANNELMSG_COUNT
>  };

For completeness, I'd like to see the channel_message_table also updated
with these new entries so that everything stays in sync and is explicitly
defined.

Michael

> 
> --
> 2.19.1