Re: [PATCH/RFC] driver core: Postpone DMA tear-down until after devres release

[John Garry]

On 26/03/2019 12:31, Geert Uytterhoeven wrote:
> Hi John,
>
> CC robh
>
> On Tue, Mar 26, 2019 at 12:42 PM John Garry <john.garry@xxxxxxxxxx> wrote:
> > > Memory is incorrectly freed using the direct ops, as dma_map_ops = NULL.
> > > Oops...
> > >
> > > After reversing the order of the calls to arch_teardown_dma_ops() and
> > > devres_release_all(), dma_map_ops is still valid, and the DMA memory is
> > > now released using __iommu_free_attrs():
> > >
> > >     +sata_rcar ee300000.sata: dmam_release:32: size 2048 vaddr ffffff8012145000 dma_handle 0x0x00000000fffff000 attrs 0x0
> > >     +sata_rcar ee300000.sata: dma_free_attrs:289: size 2048, ops = iommu_dma_ops
> > >     +sata_rcar ee300000.sata: dma_free_attrs:311: calling __iommu_free_attrs()
> > > ---
> > >  drivers/base/dd.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> > > index 8ac10af17c0043a3..d62487d024559620 100644
> > > --- a/drivers/base/dd.c
> > > +++ b/drivers/base/dd.c
> > > @@ -968,9 +968,9 @@ static void __device_release_driver(struct device *dev, struct device *parent)
> > >                       drv->remove(dev);
> > >
> > >               device_links_driver_cleanup(dev);
> > > -             arch_teardown_dma_ops(dev);
> > >
> > >               devres_release_all(dev);
> > > +             arch_teardown_dma_ops(dev);
> > >               dev->driver = NULL;
> >
> > Hi guys,
> >
> > Could there still be the same problem in the error path of really_probe():
> >
> > static int really_probe(struct device *dev, struct device_driver *drv)
> > {
> >
> >         [...]
> >
> >         goto done;
> >
> > probe_failed:
> >         arch_teardown_dma_ops(dev);
> > dma_failed:
> >         if (dev->bus)
> >                 blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
> >                                      BUS_NOTIFY_DRIVER_NOT_BOUND, dev);
> > pinctrl_bind_failed:
> >         device_links_no_driver(dev);
> >         devres_release_all(dev);
> >         driver_sysfs_remove(dev);
> >         dev->driver = NULL;
> >         dev_set_drvdata(dev, NULL);
> >
> > We seem to be able to call arch_teardown_dma_ops() prior to
> > devres_release_all() if we reach probe_failed label.
>
> Yes, this looks like another instance of the same problem.
> And test_remove doesn't expose this, as it doesn't exercise the full cycle.

Hi Geert,

OK, thanks.

There is another devres_release_all() call in device_release(). Not sure 
if there is another potential problem there also...

As for this issue, I'll look to fix unless anyone else doing it.

Cheers,
John

> Gr{oetje,eeting}s,
>
>                         Geert