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    SubjectRe: [PATCH/RFC] driver core: Postpone DMA tear-down until after devres release
    Hi John,

    CC robh

    On Tue, Mar 26, 2019 at 12:42 PM John Garry <john.garry@huawei.com> 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.

    Gr{oetje,eeting}s,

    Geert

    --
    Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

    In personal conversations with technical people, I call myself a hacker. But
    when I'm talking to journalists I just say "programmer" or something like that.
    -- Linus Torvalds

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