From: Peter Zijlstra <peterz@infradead.org>
To: Xiao Guangrong <guangrong.xiao@gmail.com>
Cc: paulmck@linux.vnet.ibm.com, rostedt@goodmis.org,
Lai Jiangshan <jiangshanlai@gmail.com>,
stefani@seibold.net,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: Is read barrier missed in kfifo?
Date: Fri, 11 May 2018 10:32:42 +0200 [thread overview]
Message-ID: <20180511083242.GJ12217@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <5382d3a8-08e0-5429-0cd3-36f9c69197e1@gmail.com>
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.
next prev parent reply other threads:[~2018-05-11 8:32 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-11 7:25 Xiao Guangrong
2018-05-11 7:33 ` Stefani Seibold
2018-05-11 8:32 ` Peter Zijlstra [this message]
2018-05-11 16:20 ` Paul E. McKenney
2018-05-14 6:57 ` Peter Zijlstra
2018-05-14 13:25 ` Paul E. McKenney
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