netdev - RE: [PATCH v2] net: fec: Fixed panic problem with non-tso

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Date:   Wed, 18 Jan 2017 05:38:27 +0000
From:   Andy Duan <fugang.duan@....com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        Yuusuke Ashiduka <ashiduka@...fujitsu.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH v2] net: fec: Fixed panic problem with non-tso

From: Eric Dumazet <eric.dumazet@...il.com> Sent: Wednesday, January 18, 2017 1:02 PM
>To: Yuusuke Ashiduka <ashiduka@...fujitsu.com>
>Cc: Andy Duan <fugang.duan@....com>; netdev@...r.kernel.org
>Subject: Re: [PATCH v2] net: fec: Fixed panic problem with non-tso
>
>On Wed, 2017-01-18 at 13:11 +0900, Yuusuke Ashiduka wrote:
>> If highmem and 2GB or more of memory are valid, "this_frag-> page.p"
>> indicates the highmem area, so the result of page_address() is NULL
>> and panic occurs.
>>
>> This commit fixes this by using the skb_frag_dma_map() helper, which
>> takes care of mapping the skb fragment properly. Additionally, the
>> type of mapping is now tracked, so it can be unmapped using
>> dma_unmap_page or dma_unmap_single when appropriate.
>
>
>I would prefer we fix the root cause, instead of tweaking all legacy drivers out
>there :/
>
>
I agree with you.

The driver always doesn't support highmem. The fragment shouldn't  allocate from highmem except the common code bug.
If request the driver to support NETIF_F_HIGHDMA feature, we also add highmem support for tso driver.

Andy