On Mon, Oct 11 2021, Halil Pasic <pasic@xxxxxxxxxxxxx> wrote:
> On Mon, 11 Oct 2021 16:33:45 +0200
> Cornelia Huck <cohuck@xxxxxxxxxx> wrote:
>
>> On Mon, Oct 11 2021, Pierre Morel <pmorel@xxxxxxxxxxxxx> wrote:
>>
>> > On 10/11/21 1:59 PM, Halil Pasic wrote:
>> >> diff --git a/drivers/s390/cio/device_ops.c b/drivers/s390/cio/device_ops.c
>> >> index 0fe7b2f2e7f5..c533d1dadc6b 100644
>> >> --- a/drivers/s390/cio/device_ops.c
>> >> +++ b/drivers/s390/cio/device_ops.c
>> >> @@ -825,13 +825,23 @@ EXPORT_SYMBOL_GPL(ccw_device_get_chid);
>> >> */
>> >> void *ccw_device_dma_zalloc(struct ccw_device *cdev, size_t size)
>> >> {
>> >> - return cio_gp_dma_zalloc(cdev->private->dma_pool, &cdev->dev, size);
>> >> + void *addr;
>> >> +
>> >> + if (!get_device(&cdev->dev))
>> >> + return NULL;
>> >> + addr = cio_gp_dma_zalloc(cdev->private->dma_pool, &cdev->dev, size);
>> >> + if (IS_ERR_OR_NULL(addr))
>> >
>> > I can be wrong but it seems that only dma_alloc_coherent() used in
>> > cio_gp_dma_zalloc() report an error but the error is ignored and used as
>> > a valid pointer.
>>
>> Hm, I thought dma_alloc_coherent() returned either NULL or a valid
>> address?
>
> Yes, that is what is documented.
>
>>
>> >
>> > So shouldn't we modify this function and just test for a NULL address here?
>>
>> If I read cio_gp_dma_zalloc() correctly, we either get NULL or a valid
>> address, so yes.
>>
>
> I don't think the extra care will hurt us too badly. I prefer to keep
> the IS_ERR_OR_NULL() check because it needs less domain specific
> knowledge to be understood, and because it is more robust.
It feels weird, though -- I'd rather have a comment that tells me
exactly what cio_gp_dma_zalloc() is supposed to return; I would have
expected that a _zalloc function always gives me a valid pointer or
NULL.
