The current implementation of futex_lock_pi returns -ERESTART_RESTARTBLOCK
in case that the lock operation has been interrupted by a signal.  This
results in a return of -EINTR to userspace in case there is an handler for
the signal.  This is wrong, because userspace expects that the lock
function does not return in any case of signal delivery.

This was not caught by my insufficient test case, but triggered a nasty
userspace problem in an high load application scenario.  Unfortunately also
glibc does not check for this invalid return value.

Using -ERSTARTNOINTR makes sure, that the interrupted syscall is restarted.
 The restart block related code can be safely removed, as the possible
timeout argument is an absolute time value.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>