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: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 908c04f..6163e4c 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -861,6 +861,8 @@
#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 @@
break;
/* try again */
- spin_unlock(&lowest_rq->lock);
+ double_unlock_balance(rq, lowest_rq);
lowest_rq = NULL;
}
@@ -1091,7 +1093,7 @@
resched_task(lowest_rq->curr);
- spin_unlock(&lowest_rq->lock);
+ double_unlock_balance(rq, lowest_rq);
ret = 1;
out:
@@ -1197,7 +1199,7 @@
}
skip:
- spin_unlock(&src_rq->lock);
+ double_unlock_balance(this_rq, src_rq);
}
return ret;