[PATCH] arm64: replace read_lock to rcu lock in call_step_hook

[Sebastian Andrzej Siewior]

* Yang Shi | 2016-02-08 14:49:24 [-0800]:

>BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:917
…
>This issue is similar with 62c6c61("arm64: replace read_lock to rcu lock in
>call_break_hook"), but comes to single_step_handler.
>
>This also solves kgdbts boot test silent hang issue on 4.4 -rt kernel.

I am going to apply this for -RT.

Sebastian