netdev - Re: [PATCH net-next RFC 2/2] tun: enable napi_gro

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Date:   Wed, 06 Sep 2017 11:01:35 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Petar Penkov <ppenkov@...gle.com>
Cc:     netdev@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
        Mahesh Bandewar <maheshb@...gle.com>,
        Willem de Bruijn <willemb@...gle.com>, davem@...emloft.net,
        ppenkov@...nford.edu
Subject: Re: [PATCH net-next RFC 2/2] tun: enable napi_gro_frags() for
 TUN/TAP driver

On Tue, 2017-09-05 at 15:35 -0700, Petar Penkov wrote:
> Add a TUN/TAP receive mode that exercises the napi_gro_frags()
> interface. This mode is available only in TAP mode, as the interface
> expects packets with Ethernet headers.
> 


Hi Petar, thanks a lot for this work.

I must confess I have to retract one feedback I gave while reviewing
your patches.


> +		local_bh_disable();
> +		data = napi_alloc_frag(fragsz);
> +		local_bh_enable();
> +		if (!data) {
> +			err = -ENOMEM;
> +			goto free;
> +		}
> +
> +		page = virt_to_page(data);
> +		offset = offset_in_page(data);

These two lines above indeed trigger too many problems in the kernel.
(Like the one you tried to cover here
https://patchwork.kernel.org/patch/9927927/ )

Please use for your next submission the code you originally had :

	page = virt_to_head_page(data);
	offset = data - page_address(page);


Thanks !