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

[John Garry <john.garry@huawei.com>]

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@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.
>

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
>