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Commit 1b12bbc7 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

lockdep: re-annotate scheduler runqueues 



Instead of using a per-rq lock class, use the regular nesting operations.

However, take extra care with double_lock_balance() as it can release the
already held rq->lock (and therefore change its nesting class).

So what can happen is:

 spin_lock(rq->lock);	// this rq subclass 0

 double_lock_balance(rq, other_rq);
   // release rq
   // acquire other_rq->lock subclass 0
   // acquire rq->lock subclass 1

 spin_unlock(other_rq->lock);

leaving you with rq->lock in subclass 1

So a subsequent double_lock_balance() call can try to nest a subclass 1
lock while already holding a subclass 1 lock.

Fix this by introducing double_unlock_balance() which releases the other
rq's lock, but also re-sets the subclass for this rq's lock to 0.

Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 64aa348e

kernel/sched.c

+9 −2
Original line number Diff line number Diff line
@@ -2812,6 +2812,13 @@ static int double_lock_balance(struct rq *this_rq, struct rq *busiest) 
	return ret;

}



static void double_unlock_balance(struct rq *this_rq, struct rq *busiest)

	__releases(busiest->lock)

{

	spin_unlock(&busiest->lock);

	lock_set_subclass(&this_rq->lock.dep_map, 0, _RET_IP_);

}



/*

 * If dest_cpu is allowed for this process, migrate the task to it.

 * This is accomplished by forcing the cpu_allowed mask to only
@@ -3636,7 +3643,7 @@ load_balance_newidle(int this_cpu, struct rq *this_rq, struct sched_domain *sd, 
		ld_moved = move_tasks(this_rq, this_cpu, busiest,

					imbalance, sd, CPU_NEWLY_IDLE,

					&all_pinned);

		spin_unlock(&busiest->lock);

		double_unlock_balance(this_rq, busiest);



		if (unlikely(all_pinned)) {

			cpu_clear(cpu_of(busiest), *cpus);
@@ -3751,7 +3758,7 @@ static void active_load_balance(struct rq *busiest_rq, int busiest_cpu) 
		else

			schedstat_inc(sd, alb_failed);

	}

	spin_unlock(&target_rq->lock);

	double_unlock_balance(busiest_rq, target_rq);

}



#ifdef CONFIG_NO_HZ

kernel/sched_rt.c

+5 −3
Original line number Diff line number Diff line
@@ -861,6 +861,8 @@ static void put_prev_task_rt(struct rq *rq, struct task_struct *p) 
#define RT_MAX_TRIES 3



static int double_lock_balance(struct rq *this_rq, struct rq *busiest);

static void double_unlock_balance(struct rq *this_rq, struct rq *busiest);



static void deactivate_task(struct rq *rq, struct task_struct *p, int sleep);



static int pick_rt_task(struct rq *rq, struct task_struct *p, int cpu)
@@ -1022,7 +1024,7 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq) 
			break;



		/* try again */

		spin_unlock(&lowest_rq->lock);

		double_unlock_balance(rq, lowest_rq);

		lowest_rq = NULL;

	}
@@ -1091,7 +1093,7 @@ static int push_rt_task(struct rq *rq) 


	resched_task(lowest_rq->curr);



	spin_unlock(&lowest_rq->lock);

	double_unlock_balance(rq, lowest_rq);



	ret = 1;

out:
@@ -1197,7 +1199,7 @@ static int pull_rt_task(struct rq *this_rq) 


		}

 skip:

		spin_unlock(&src_rq->lock);

		double_unlock_balance(this_rq, src_rq);

	}



	return ret;