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

[Geert Uytterhoeven]

Hi Robin,

On Fri, Feb 8, 2019 at 6:55 PM Robin Murphy <robin.murphy@xxxxxxx> wrote:
> On 08/02/2019 16:40, Joerg Roedel wrote:
> > On Thu, Feb 07, 2019 at 08:36:53PM +0100, Geert Uytterhoeven wrote:
> >> 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;
> >>              dev_set_drvdata(dev, NULL);
> >>              if (dev->pm_domain && dev->pm_domain->dismiss)
> >
> > Thanks for the fix! Should it also be tagged for stable and get a Fixes

FTR, Greg has added it to driver-core-testing, with a CC to stable.

> > tag? I know it only triggers with a fix in v5.0-rc, but still...
>
> I think so:
>
> Fixes: 09515ef5ddad ("of/acpi: Configure dma operations at probe time
> for platform/amba/pci bus devices")

Thanks! It won't backport cleanly due to commit dc3c05504d38849f
("dma-mapping: remove dma_deconfigure") in v4.20, though.

> There aren't many drivers using dmam_alloc_*(), let alone which would
> also find themselves behind an IOMMU on an Arm system, but it turns out
> I actually have another one which can reproduce the BUG() with 5.0-rc.

SATA core uses dmam_alloc_*().

> I've tried a 4.12 kernel with a bit of instrumentation[1] and sure
> enough the devres-managed buffer is freed with the wrong ops[2] even
> then. How it manages not to blow up more catastrophically I have no
> idea... I guess at best it just leaks the buffers and IOMMU mappings,
> and at worst quietly frees random other pages instead.

May depend on the actual ops, and whether CMA is used or not.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

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