Messages in this thread | | | Subject | Re: question on read_barrier_depends | From | Oliver Neukum <> | Date | Fri, 18 Apr 2014 19:17:43 +0200 |
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On Thu, 2014-04-17 at 11:50 -0400, Alan Stern wrote: > On Thu, 17 Apr 2014, Oliver Neukum wrote: > > > On Wed, 2014-04-16 at 11:26 -0400, Alan Stern wrote: > > > > > In addition, the following code in kfifo_get() does this: > > > > > > *(typeof(__tmp->type))__val = \ > > > (__is_kfifo_ptr(__tmp) ? \ > > > ((typeof(__tmp->type))__kfifo->data) : \ > > > (__tmp->buf) \ > > > )[__kfifo->out & __tmp->kfifo.mask]; \ > > > smp_wmb(); \ > > > __kfifo->out++; \ > > > > > > It looks like the smp_wmb() should really be smp_mb(), because it > > > separates the _read_ for val from the _write_ of kfifo->out. > > > > But where is kfifo->out read at all? > > It is read in kfifo_put(), inside the call to kfifo_is_full() -> > kfifo_len().
I had overlooked that. In that case kfifo_put() also needs smp_read_barrier_depends()
Regards Oliver
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