[RFC PATCH 2/2 with seqcount v3] reservation: add suppport for read-only access using rcu

[Maarten Lankhorst]

op 23-04-14 13:15, Maarten Lankhorst schreef:
> This adds 4 more functions to deal with rcu.
>
> reservation_object_get_fences_rcu() will obtain the list of shared
> and exclusive fences without obtaining the ww_mutex.
>
> reservation_object_wait_timeout_rcu() will wait on all fences of the
> reservation_object, without obtaining the ww_mutex.
>
> reservation_object_test_signaled_rcu() will test if all fences of the
> reservation_object are signaled without using the ww_mutex.
>
> reservation_object_get_excl() is added because touching the fence_excl
> member directly will trigger a sparse warning.
>
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst at canonical.com>
> ---
> Using seqcount and fixing some lockdep bugs.
> Changes since v2:
> - Fix some crashes, remove some unneeded barriers when provided by seqcount 
> writes
> - Fix code to work correctly with sparse's RCU annotations.
> - Create a global string for the seqcount lock to make lockdep happy.
>
> Can I get this version reviewed? If it looks correct I'll mail the full series
> because it's intertwined with the TTM conversion to use this code.
Ping, can anyone review this?