linux-kernel - Re: [PATCH v2 0/4] mm/gup, drm/i915: refactor gup_fast, convert to pin_user

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Date:   Sat, 23 May 2020 15:33:47 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Chris Wilson <chris@...is-wilson.co.uk>,
        Andrew Morton <akpm@...ux-foundation.org>
CC:     Souptick Joarder <jrdr.linux@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Tvrtko Ursulin <tvrtko.ursulin@...el.com>,
        Matthew Auld <matthew.auld@...el.com>,
        <intel-gfx@...ts.freedesktop.org>,
        <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>
Subject: Re: [PATCH v2 0/4] mm/gup, drm/i915: refactor gup_fast, convert to
 pin_user_pages()

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@build.alporthouse.com
> 
> 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@...is-wilson.co.uk>
> -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