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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