Messages in this thread | | | Date | Fri, 11 May 2018 09:20:53 -0700 | From | "Paul E. McKenney" <> | Subject | Re: Is read barrier missed in kfifo? |
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On Fri, May 11, 2018 at 10:32:42AM +0200, Peter Zijlstra wrote: > 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.
Isn't this one of the places where we rely on control dependencies?
Thanx, Paul
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