A set of PI futex fixes:
- Address a longstanding issue where the user space part of the PI futex
is not writeable. The kernel returns with inconsistent state which can
in the worst case result in a UAF of a tasks kernel stack. The solution
is to establish consistent kernel state which makes future operations
on the futex fail because user space and kernel space state are
inconsistent. Not a problem as PI futexes fundamentaly require a
functional RW mapping and if user space pulls the rug under it, then it
can keep the pieces it asked for.
- Address an issue where the return value is incorrect in case that the
futex was acquired after a timeout/signal made the waiter drop out of
the rtmutex wait. In one of the corner cases the kernel returned an
error code despite having successfully acquired the futex.