Re: [dpdk-dev] [PATCH v3 0/6] use IOVAs check based on DMA mask

[Alejandro Lucero <alejandro.lucero@netronome.com>]

On Tue, Oct 30, 2018 at 10:19 AM Burakov, Anatoly <anatoly.burakov@intel.com>
wrote:

> On 29-Oct-18 11:39 AM, Alejandro Lucero wrote:
> > I got a patch that solves a bug when calling rte_eal_dma_mask using the
> > mask instead of the maskbits. However, this does not solves the deadlock.
> >
> > Interestingly, the problem looks like a compiler one. Calling
> > rte_memseg_walk does not return when calling inside rt_eal_dma_mask, but
> > if you modify the call like this:
> >
> > *diff --git a/lib/librte_eal/common/eal_common_memory.c
> > b/lib/librte_eal/common/eal_common_memory.c*
> >
> > *index 12dcedf5c..69b26e464 100644*
> >
> > *--- a/lib/librte_eal/common/eal_common_memory.c*
> >
> > *+++ b/lib/librte_eal/common/eal_common_memory.c*
> >
> > @@ -462,7 +462,7 @@rte_eal_check_dma_mask(uint8_t maskbits)
> >
> > /* create dma mask */
> >
> > mask = ~((1ULL << maskbits) - 1);
> >
> > - if (rte_memseg_walk(check_iova, &mask))
> >
> > +if (!rte_memseg_walk(check_iova, &mask))
> >
> > /*
> >
> > * Dma mask precludes hugepage usage.
> >
> > * This device can not be used and we do not need to keep
> >
> >
> > it works, although the value returned to the invoker changes, of course.
> > But the point here is it should be the same behaviour when calling
> > rte_memseg_walk than before and it is not.
> >
> >
> > Anatoly, maybe you can see something I can not.
> >
>
> memseg walk will return 0 only when each callback returned 0 and there
> were no more segments left to call callbacks on. If your code always
> returns 0, then return value of memseg_walk will always be zero.
>
> If your code returns 1 or -1 in some cases, then this error condition
> will trigger. If it doesn't, then your condition by which you decide to
> return 1 or 0, is incorrect :) I couldn't spot any obvious issues there,
> but i'll recheck.
>
>
Thanks for looking at this, but I was wrong. The return code changes
everything so it does not make sense to compare both.

-- 
> Thanks,
> Anatoly
>