Re: [v4.14.y PATCH 0/2] fix drm/udl use-after-free error

[Sasha Levin <sashal@kernel.org>]

On Tue, Jul 16, 2019 at 10:08:28AM -0600, Ross Zwisler wrote:
>On Mon, Jul 15, 2019 at 09:13:08PM -0400, Sasha Levin wrote:
>> On Mon, Jul 15, 2019 at 01:36:16PM -0600, Ross Zwisler wrote:
>> > This patch is the second in this series, and requires the first patch as
>> > a dependency.  This series apples cleanly to v4.14.133.
>>
>> Hm, we don't need ac3b35f11a06 here? Why not? I'd love to document that
>> with the backport.
>
>Nope, we don't need that patch in the v4.14 backport.
>
>In v4.19.y we have two functions, drm_dev_put() and drm_dev_unref(), which are
>aliases for one another (drm_dev_unref() just calls drm_dev_put()).
>drm_dev_unref() is the older of the two, and was introduced back in v4.0.
>drm_dev_put() was introduced in v4.15 with
>
>9a96f55034e41 drm: introduce drm_dev_{get/put} functions
>
>and slowly callers were moved from the old name (_unref) to the new name
>(_put).  The patch you mentioned, ac3b35f11a06, is one such patch where we are
>replacing a drm_dev_unref() call with a drm_dev_put() call.  This doesn't have
>a functional change, but was necessary so that the third patch in the v4.19.y
>series I sent would apply cleanly.
>
>For the v4.14.y series, though, the drm_dev_put() function hasn't yet been
>defined and everyone is still using drm_dev_unref().  So, we don't need a
>backport of ac3b35f11a06, and I also had a small backport change in the last
>patch of the v4.14.y series where I had to change a drm_dev_put() call with a
>drm_dev_unref() call.
>
>Just for posterity, the drm_dev_unref() calls were eventually all changed to
>drm_dev_put() in v5.0, and drm_dev_unref() was removed entirely.  That
>happened with the following two patches:
>
>808bad32ea423 drm: replace "drm_dev_unref" function with "drm_dev_put"
>ba1d345401476 drm: remove deprecated "drm_dev_unref" function

Thank you for the explanation. I've queued both this and the 4.19
patches, and added your explanation to the 4.14 patch.

--
Thanks,
Sasha