linux-kernel - Re: [PATCH net-next 05/12] ptr_ring: disallow lockless __ptr_ring

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Date:   Mon, 29 Jan 2018 11:36:09 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        John Fastabend <john.fastabend@...il.com>,
        David Miller <davem@...emloft.net>
Subject: Re: [PATCH net-next 05/12] ptr_ring: disallow lockless
 __ptr_ring_full



On 2018年01月26日 10:46, Michael S. Tsirkin wrote:
>> On 2018年01月26日 07:36, Michael S. Tsirkin wrote:
>>> Similar to bcecb4bbf88a ("net: ptr_ring: otherwise safe empty checks can
>>> overrun array bounds") a lockless use of __ptr_ring_full might
>>> cause an out of bounds access.
>>>
>>> We can fix this, but it's easier to just disallow lockless
>>> __ptr_ring_full for now.
>> It looks to me that just fix this is better than disallow through doc (which
>> is easily to be ignored ...).
>>
>> Thanks
> lockless is tricky, and I'd rather not sprinkle READ/WRITE_ONCE where
> they aren't necessary.
>

The problem is then API looks a little bit strange. Lockless were only 
allowed to be done at __ptr_ring_empty() but not __ptr_ring_full().

Thanks