locking/rwsem-spinlock: Add killable versions of __down_read()

Rename __down_read() in __down_read_common() and teach it
to abort waiting in case of pending signals and killable
state argument passed.

Note, that we shouldn't wake anybody up in EINTR path, as:

We check for signal_pending_state() after (!waiter.task)
test and under spinlock. So, current task wasn't able to
be woken up. It may be in two cases: a writer is owner
of the sem, or a writer is a first waiter of the sem.

If a writer is owner of the sem, no one else may work
with it in parallel. It will wake somebody, when it
call up_write() or downgrade_write().

If a writer is the first waiter, it will be woken up,
when the last active reader releases the sem, and
sem->count became 0.

Also note, that set_current_state() may be moved down
to schedule() (after !waiter.task check), as all
assignments in this type of semaphore (including wake_up),
occur under spinlock, so we can't miss anything.

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: arnd@arndb.de
Cc: avagin@virtuozzo.com
Cc: davem@davemloft.net
Cc: fenghua.yu@intel.com
Cc: gorcunov@virtuozzo.com
Cc: heiko.carstens@de.ibm.com
Cc: hpa@zytor.com
Cc: ink@jurassic.park.msu.ru
Cc: mattst88@gmail.com
Cc: rth@twiddle.net
Cc: schwidefsky@de.ibm.com
Cc: tony.luck@intel.com
Link: http://lkml.kernel.org/r/149789533283.9059.9829416940494747182.stgit@localhost.localdomain


Signed-off-by: Ingo Molnar <mingo@kernel.org>