futex needs __get_user_pages_fast implementation

[Zi Shen Lim]

Futex uses GUP. Currently on ARM, the default __get_user_pages_fast being used always returns 0, leading to a forever loop in get_futex_key.

[Zi Shen Lim (zlim)]

Steve Capper (LEG) is working on GUP.

[Mike Holmes (mike-holmes)]

Steve Cappers fix has been applied to the LNG kernel, but the fix has not been applied upstream yet.

[Steve Capper (steve-capper)]

I've posted an RFC to lakml:
http://lists.infradead.org/pipermail/linux-arm-kernel/2013-October/205951.html

[Mike Holmes (mike-holmes)]

Latest version of this patch should be applied to the LNG kernel when it is updated to the latest RT patch in the 13.11 cycle.

[Gary S. Robertson (gary-robertson)]

Steve Capper's patches to address this were applied to the LNG kernels in time for the 13.10 release cycle.

I compared the contents of these applied patches line for line with the RFC submissions in the link posted in comment #3 for this bug. Other than some minor differences in line numbering in some new files, the content of the already-applied patches is identical to the content of the patches submitted for comment.

AFAIK there have been no comments on the patches as submitted upstream, nor am I aware that those patches have been accepted and applied to the upstream kernel as yet. Consequently at this time I am disinclined to take any action to replace the patches already applied to the LNG kernels with their counterparts from the RFC link in comment #3.

At such time as the patches are applied upstream I will be happy to revert our local commits in order to avoid future merge conflicts with upstream kernel updates. Then we can either cherry-pick or simply merge the patches from upstream.