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

Alejandro Lucero alejandro.lucero at netronome.com
Mon Oct 29 15:35:04 CET 2018


On Mon, Oct 29, 2018 at 2:18 PM Thomas Monjalon <thomas at monjalon.net> wrote:

> 29/10/2018 14:40, Alejandro Lucero:
> > On Mon, Oct 29, 2018 at 1:18 PM Yao, Lei A <lei.a.yao at intel.com> wrote:
> > > *From:* Alejandro Lucero [mailto:alejandro.lucero at netronome.com]
> > > On Mon, Oct 29, 2018 at 11:46 AM Thomas Monjalon <thomas at monjalon.net>
> > > wrote:
> > >
> > > 29/10/2018 12:39, Alejandro Lucero:
> > > > 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.
> > >
> > > The deadlock is a bigger concern I think.
> > >
> > > I think once the call to rte_eal_check_dma_mask uses the maskbits
> instead
> > > of the mask, calling rte_memseg_walk_thread_unsafe avoids the deadlock.
> > >
> > > Yao, can you try with the attached patch?
> > >
> > > Hi, Lucero
> > >
> > > This patch can fix the issue at my side. Thanks a lot
> > > for you quick action.
> >
> > Great!
> >
> > I will send an official patch with the changes.
>
> Please, do not forget my other request to better comment functions.
>
>
>
Sure.


> > I have to say that I tested the patchset, but I think it was where
> > legacy_mem was still there and therefore dynamic memory allocation code
> not
> > used during memory initialization.
> >
> > There is something that concerns me though. Using
> > rte_memseg_walk_thread_unsafe could be a problem under some situations
> > although those situations being unlikely.
> >
> > Usually, calling rte_eal_check_dma_mask happens during initialization.
> Then
> > it is safe to use the unsafe function for walking memsegs, but with
> device
> > hotplug and dynamic memory allocation, there exists a potential race
> > condition when the primary process is allocating more memory and
> > concurrently a device is hotplugged and a secondary process does the
> device
> > initialization. By now, this is just a problem with the NFP, and the
> > potential race condition window really unlikely, but I will work on this
> > asap.
>
> Yes, this is what concerns me.
> You can add a comment explaining the unsafe which is not handled.
>
>
I'' do.

Thanks!


>
> > > > 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:
> > > >
> > > > -       if (rte_memseg_walk(check_iova, &mask))
> > > > +       if (!rte_memseg_walk(check_iova, &mask))
> > > >
> > > > 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.
> > >
> > > Anyway, the coding style requires to save the return value in a
> variable,
> > > instead of nesting the call in an "if" condition.
> > > And the "if" check should be explicitly != 0 because it is not a real
> > > boolean.
> > >
> > > PS: please do not top post and avoid HTML emails, thanks
> > >
> > >
> >
>
>
>
>
>
>


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