netdev - RE: [PATCH] hv_netvsc: Make sure out channel is fully opened on send

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Message-ID: <BN6PR21MB01612C60B5421AF2BB09742CCA150@BN6PR21MB0161.namprd21.prod.outlook.com>
Date:   Wed, 26 Sep 2018 17:13:24 +0000
From:   Haiyang Zhang <haiyangz@...rosoft.com>
To:     Mohammed Gamal <mgamal@...hat.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     KY Srinivasan <kys@...rosoft.com>, vkuznets <vkuznets@...hat.com>,
        "otubo@...hat.com" <otubo@...hat.com>, cavery <cavery@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devel@...uxdriverproject.org" <devel@...uxdriverproject.org>
Subject: RE: [PATCH] hv_netvsc: Make sure out channel is fully opened on send



> -----Original Message-----
> From: Mohammed Gamal <mgamal@...hat.com>
> Sent: Wednesday, September 26, 2018 12:34 PM
> To: Stephen Hemminger <sthemmin@...rosoft.com>; netdev@...r.kernel.org
> Cc: KY Srinivasan <kys@...rosoft.com>; Haiyang Zhang
> <haiyangz@...rosoft.com>; vkuznets <vkuznets@...hat.com>;
> otubo@...hat.com; cavery <cavery@...hat.com>; linux-
> kernel@...r.kernel.org; devel@...uxdriverproject.org; Mohammed Gamal
> <mgamal@...hat.com>
> Subject: [PATCH] hv_netvsc: Make sure out channel is fully opened on send
> 
> Dring high network traffic changes to network interface parameters such as
> number of channels or MTU can cause a kernel panic with a NULL pointer
> dereference. This is due to netvsc_device_remove() being called and
> deallocating the channel ring buffers, which can then be accessed by
> netvsc_send_pkt() before they're allocated on calling
> netvsc_device_add()
> 
> The patch fixes this problem by checking the channel state and returning
> ENODEV if not yet opened. We also move the call to hv_ringbuf_avail_percent()
> which may access the uninitialized ring buffer.
> 
> Signed-off-by: Mohammed Gamal <mgamal@...hat.com>
> ---
>  drivers/net/hyperv/netvsc.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/hyperv/netvsc.c b/drivers/net/hyperv/netvsc.c index
> fe01e14..75f1b31 100644
> --- a/drivers/net/hyperv/netvsc.c
> +++ b/drivers/net/hyperv/netvsc.c
> @@ -825,7 +825,12 @@ static inline int netvsc_send_pkt(
>  	struct netdev_queue *txq = netdev_get_tx_queue(ndev, packet->q_idx);
>  	u64 req_id;
>  	int ret;
> -	u32 ring_avail = hv_get_avail_to_write_percent(&out_channel-
> >outbound);
> +	u32 ring_avail;
> +
> +	if (out_channel->state != CHANNEL_OPENED_STATE)
> +		return -ENODEV;
> +
> +	ring_avail = hv_get_avail_to_write_percent(&out_channel->outbound);

When you reproducing the NULL ptr panic, does your kernel include the following patch?
hv_netvsc: common detach logic
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=7b2ee50c0cd513a176a26a71f2989facdd75bfea

We call netif_tx_disable(ndev) and netif_device_detach(ndev) before doing the changes 
on MTU or #channels. So there should be no call to start_xmit() when channel is not ready.

If you see the check for CHANNEL_OPENED_STATE is still necessary on upstream kernel (including 
the patch " common detach logic "), we should debug further on the code and find out the 
root cause.

Thanks,
- Haiyang