Re: Is read barrier missed in kfifo?

[Peter Zijlstra]

On Fri, May 11, 2018 at 03:25:18PM +0800, Xiao Guangrong wrote:
> 
> Hi,
> 
> Currently, there is no read barrier between reading the index
> (kfifo.in) and fetching the real data from the fifo.
> 
> I am afraid that will cause the vfifo is observed as not empty
> however the data is not actually ready for read. Right?

That code is decidedly dodgy indeed. I can only see smp_wmb() but no
matching barriers at all -- therefore the code is almost certainly as
good as not having any barriers at all.

I would suggest you try and convert the code to smp_store_release() and
smp_load_acquire() while you're at it.