Re: [PATCH 4/4] dma-mapping: clear dev->dma_ops in arch_teardown_dma_ops

[Michael Ellerman <mpe@ellerman.id.au>]

Guenter Roeck <linux@roeck-us.net> writes:
> Hi,
>
> On Mon, Aug 27, 2018 at 10:47:11AM +0200, Christoph Hellwig wrote:
>> There is no reason to leave the per-device dma_ops around when
>> deconfiguring a device, so move this code from arm64 into the
>> common code.
>> Signed-off-by: Christoph Hellwig <hch@lst.de>
>> Reviewed-by: Robin Murphy <robin.murphy@arm.com>
>
> This patch causes various ppc images to crash in -next due to NULL
> DMA ops in dma_alloc_attrs().

I finally remembered where you autobuilder is :)

https://kerneltests.org/builders/qemu-ppc-next/builds/970/steps/qemubuildcommand_1/logs/stdio

Looks like mac99 at least is failing.

Just reproduced it on my setup.

> Looking into the code, the macio driver tries to instantiate on
> the 0000:f0:0d.0 PCI address (the driver maps to all Apple PCI IDs)
> and fails. This results in a call to arch_teardown_dma_ops(). Later,
> the same device pointer is used to instantiate ohci-pci, which
> crashes in probe because the dma_ops pointer has been cleared.
>
> I don't claim to fully understand the code, but to me it looks like
> the pci device is allocated and waiting for a driver to attach to.
> See arch/powerpc/kernel/pci_of_scan.c:of_create_pci_dev().
> If attaching a driver (here: macio) fails, the same device pointer
> is then reused for the next matching driver until a match is found
> and the device is successfully instantiated. Of course this fails
> quite badly if the device pointer has been scrubbed after the first
> failure.
>
> I don't know if this is generic PCI behavior or ppc specific.
> I am copying pci and ppc maintainers for additional input.

I would guess this is some PPC special sauce  O_o

Will have a look.

cheers