sched/numa: Fix use of spin_{un}lock_irq() when interrupts are disabled

As Peter Zijlstra told me, we have the following path:

do_exit()
  exit_itimers()
    itimer_delete()
      spin_lock_irqsave(&timer->it_lock, &flags);
      timer_delete_hook(timer);
        kc->timer_del(timer) := posix_cpu_timer_del()
          put_task_struct()
            __put_task_struct()
              task_numa_free()
                spin_lock(&grp->lock);

Which means that task_numa_free() can be called with interrupts
disabled, which means that we should not be using spin_lock_irq() but
spin_lock_irqsave() instead. Otherwise we are enabling interrupts while
holding an interrupt unsafe lock!
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner<tglx@linutronix.de>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140527182541.GH11096@twins.programming.kicks-ass.netSigned-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/fair.c

@@ -1707,18 +1707,19 @@ static void task_numa_group(struct task_struct *p, int cpupid, int flags,
 void task_numa_free(struct task_struct *p)
 {
 	struct numa_group *grp = p->numa_group;
-	int i;
 	void *numa_faults = p->numa_faults_memory;
+	unsigned long flags;
+	int i;
 
 	if (grp) {
-		spin_lock_irq(&grp->lock);
+		spin_lock_irqsave(&grp->lock, flags);
 		for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++)
 			grp->faults[i] -= p->numa_faults_memory[i];
 		grp->total_faults -= p->total_numa_faults;
 
 		list_del(&p->numa_entry);
 		grp->nr_tasks--;
-		spin_unlock_irq(&grp->lock);
+		spin_unlock_irqrestore(&grp->lock, flags);
 		rcu_assign_pointer(p->numa_group, NULL);
 		put_numa_group(grp);
 	}