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Date:   Sat, 23 May 2020 15:33:47 -0700
From:   John Hubbard <>
To:     Chris Wilson <>,
        Andrew Morton <>
CC:     Souptick Joarder <>,
        Matthew Wilcox <>,
        Jani Nikula <>,
        Joonas Lahtinen <>,
        Rodrigo Vivi <>,
        David Airlie <>,
        Daniel Vetter <>,
        Tvrtko Ursulin <>,
        Matthew Auld <>,
        LKML <>, <>
Subject: Re: [PATCH v2 0/4] mm/gup, drm/i915: refactor gup_fast, convert to

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]
> Ran this through our CI, warn and subsequent lockup were gone. That
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; s=n1;
	t=1590273216; bh=oK85oUq4LCrgTs8kxvJryKE7a7GUQfAveFtGpNOU2dQ=;

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

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 a separate
patch. :)

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

John Hubbard

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