linux-kernel - Re: [PATCH] hv: do not lose pending heartbeat vmbus packets

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Message-ID: <87lgyb3vt1.fsf@vitty.brq.redhat.com>
Date:   Thu, 29 Sep 2016 11:22:02 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     "K. Y. Srinivasan" <kys@...rosoft.com>,
        Long Li <longli@...hange.microsoft.com>
Cc:     Haiyang Zhang <haiyangz@...rosoft.com>,
        devel@...uxdriverproject.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hv: do not lose pending heartbeat vmbus packets

Long Li <longli@...hange.microsoft.com> writes:

> From: Long Li <longli@...rosoft.com>
>
> The host keeps sending heartbeat packets independent of guest responding to them. In some situations, there might be multiple heartbeat packets pending in the ring buffer. Don't lose them, read them all.
>
> Signed-off-by: Long Li <longli@...rosoft.com>

Long, K. Y.,

it seems this patch didn't make it to char-misc tree and it looks like
an important fix. A couple of nitpicks below,

> ---
>  drivers/hv/hv_util.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/hv/hv_util.c b/drivers/hv/hv_util.c
> index d5acaa2..9dc6372 100644
> --- a/drivers/hv/hv_util.c
> +++ b/drivers/hv/hv_util.c
> @@ -283,10 +283,14 @@ static void heartbeat_onchannelcallback(void *context)
>  	u8 *hbeat_txf_buf = util_heartbeat.recv_buffer;
>  	struct icmsg_negotiate *negop = NULL;
>
> -	vmbus_recvpacket(channel, hbeat_txf_buf,
> -			 PAGE_SIZE, &recvlen, &requestid);
> +	while (1) {
> +
> +		vmbus_recvpacket(channel, hbeat_txf_buf,
> +				 PAGE_SIZE, &recvlen, &requestid);

We should check vmbus_recvpacket() return value as
well. E.g. hv_ringbuffer_read() may return -EAGAIN in case we didn't
receive the whole packet (and we do this check in other drivers, see
storvsc_on_channel_callback() for example).

> +
> +		if (!recvlen)

so this should be 'if (ret || !recvlen)'

> +			break;
>
> -	if (recvlen > 0) {
>  		icmsghdrp = (struct icmsg_hdr *)&hbeat_txf_buf[
>  				sizeof(struct vmbuspipe_hdr)];

-- 
  Vitaly