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

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Date:   Fri, 26 Jan 2018 10:38:05 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>, linux-kernel@...r.kernel.org
Cc:     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 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

>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
>   include/linux/ptr_ring.h | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
> index 9a72d8f..f175846 100644
> --- a/include/linux/ptr_ring.h
> +++ b/include/linux/ptr_ring.h
> @@ -45,9 +45,10 @@ struct ptr_ring {
>   };
>   
>   /* Note: callers invoking this in a loop must use a compiler barrier,
> - * for example cpu_relax().  If ring is ever resized, callers must hold
> - * producer_lock - see e.g. ptr_ring_full.  Otherwise, if callers don't hold
> - * producer_lock, the next call to __ptr_ring_produce may fail.
> + * for example cpu_relax().
> + *
> + * NB: this is unlike __ptr_ring_empty in that callers must hold producer_lock:
> + * see e.g. ptr_ring_full.
>    */
>   static inline bool __ptr_ring_full(struct ptr_ring *r)
>   {