ipc/sem: Rework semaphore wakeups

Current sysv sems have a weird ass wakeup scheme that involves keeping
preemption disabled over a potential O(n^2) loop and busy waiting on
that on other CPUs.

Kill this and simply wake the task directly from under the sem_lock.

This was discovered by a migrate_disable() debug feature that
disallows:

  spin_lock();
  preempt_disable();
  spin_unlock()
  preempt_enable();

Cc: Manfred Spraul <manfred@colorfullife.com>
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Reported-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Manfred Spraul <manfred@colorfullife.com>
Link: http://lkml.kernel.org/r/1315994224.5040.1.camel@twins
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

0 files changed, 0 insertions, 0 deletions