sched/core: Make dl_b->lock IRQ safe

Fix this lockdep warning:

[   44.804600] =========================================================
[   44.805746] [ INFO: possible irq lock inversion dependency detected ]
[   44.805746] 3.14.0-rc2-test+ hardkernel#14 Not tainted
[   44.805746] ---------------------------------------------------------
[   44.805746] bash/3674 just changed the state of lock:
[   44.805746]  (&dl_b->lock){+.....}, at: [<ffffffff8106ad15>] sched_rt_handler+0x132/0x248
[   44.805746] but this lock was taken by another, HARDIRQ-safe lock in the past:
[   44.805746]  (&rq->lock){-.-.-.}

and interrupts could create inverse lock ordering between them.

[   44.805746]
[   44.805746] other info that might help us debug this:
[   44.805746]  Possible interrupt unsafe locking scenario:
[   44.805746]
[   44.805746]        CPU0                    CPU1
[   44.805746]        ----                    ----
[   44.805746]   lock(&dl_b->lock);
[   44.805746]                                local_irq_disable();
[   44.805746]                                lock(&rq->lock);
[   44.805746]                                lock(&dl_b->lock);
[   44.805746]   <Interrupt>
[   44.805746]     lock(&rq->lock);

by making dl_b->lock acquiring always IRQ safe.

Cc: Ingo Molnar <[email protected]>
Signed-off-by: Juri Lelli <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Thomas Gleixner <[email protected]>

kernel/sched/core.c

@@ -7422,6 +7422,7 @@ static int sched_dl_global_constraints(void)
 	u64 period = global_rt_period();
 	u64 new_bw = to_ratio(period, runtime);
 	int cpu, ret = 0;
+	unsigned long flags;
 
 	/*
 	 * Here we want to check the bandwidth not being set to some
@@ -7435,10 +7436,10 @@ static int sched_dl_global_constraints(void)
 	for_each_possible_cpu(cpu) {
 		struct dl_bw *dl_b = dl_bw_of(cpu);
 
-		raw_spin_lock(&dl_b->lock);
+		raw_spin_lock_irqsave(&dl_b->lock, flags);
 		if (new_bw < dl_b->total_bw)
 			ret = -EBUSY;
-		raw_spin_unlock(&dl_b->lock);
+		raw_spin_unlock_irqrestore(&dl_b->lock, flags);
 
 		if (ret)
 			break;
@@ -7451,6 +7452,7 @@ static void sched_dl_do_global(void)
 {
 	u64 new_bw = -1;
 	int cpu;
+	unsigned long flags;
 
 	def_dl_bandwidth.dl_period = global_rt_period();
 	def_dl_bandwidth.dl_runtime = global_rt_runtime();
@@ -7464,9 +7466,9 @@ static void sched_dl_do_global(void)
 	for_each_possible_cpu(cpu) {
 		struct dl_bw *dl_b = dl_bw_of(cpu);
 
-		raw_spin_lock(&dl_b->lock);
+		raw_spin_lock_irqsave(&dl_b->lock, flags);
 		dl_b->bw = new_bw;
-		raw_spin_unlock(&dl_b->lock);
+		raw_spin_unlock_irqrestore(&dl_b->lock, flags);
 	}
 }