netdev - Re: Question on ptr

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Message-ID: <20190131093342-mutt-send-email-mst@kernel.org>
Date:   Thu, 31 Jan 2019 09:39:34 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     fei phung <feiphung27@...il.com>
Cc:     feiphung@...mail.com, netdev@...r.kernel.org
Subject: Re: Question on ptr_ring linux header

On Thu, Jan 31, 2019 at 01:16:31PM +0800, fei phung wrote:
> Hi,
> 
> /*
>  * Filename: circ_ring.c
>  * Version: 1.0
>  * Description: A circular buffer using API from
>  * https://github.com/torvalds/linux/blob/master/include/linux/ptr_ring.h
>  */
> 
> ptr_ring's void** queue is just giving data race problem, running
> consume() together with [assignment of pointers+produce()] will
> definitely give rise to data race
> 
> mutex or lock cannot help in this case. Please correct me if wrong
> 
> Regards,
> Phung

I am not sure what does assignment of pointers mean in this context.
ptr_ring is designed for a single producer and a single consumer.  For
why it works see explanation about data dependencies in
Documentation/memory-barriers.txt.  You will have to be more specific
about the data race that you see if you expect more specific answers.

Thanks,

-- 
MST