Re: [PATCH v2 0/4] mm/gup, drm/i915: refactor gup_fast, convert to pin_user_pages()

[John Hubbard]

On 2020-05-23 02:41, Chris Wilson wrote:
> Quoting John Hubbard (2020-05-22 06:19:27)
> > The purpose of posting this series is to launch a test in the
> > intel-gfx-ci tree. (The patches have already been merged into Andrew's
> > linux-mm tree.)
> >
> > This applies to today's linux.git (note the base-commit tag at the
> > bottom).
> >
> > Changes since V1:
> >
> > * Fixed a bug in the refactoring patch: added FOLL_FAST_ONLY to the
> >    list of gup_flags *not* to WARN() on. This lead to a failure in the
> >    first intel-gfx-ci test run [1].
> >
> > [1] https://lore.kernel.org/r/159008745422.32320.5724805750977048669@xxxxxxxxxxxxxxxxxxxxx
>
> Ran this through our CI, warn and subsequent lockup were gone. That
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Yea! Thanks again for these test runs. I really don't like posting
patches that I can't run-time test, but this CI system mitigates
that pretty well.


> lockup is worrying me now, but that doesn't seem to be an issue from
> this series.


I do think it's worth following up on. And it seems like it would be
very easy to repro: just hack in a forced failure at the call site of
pin_user_pages_fast_only(), and follow the breadcrumbs.


> The i915 changes were simple enough, I would have computed the pin flags
> just once (since the readonly bit is static, that would be interesting
> if that was allowed to change mid gup :)
> Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> -Chris

Thanks for the review! And if lifting that check up higher in the call
stack is desired, I'm all in favor of that being done...in a separate
patch. :)

I'm trying to keep a very light touch when converting these call sites.

thanks,
--
John Hubbard
NVIDIA