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>
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2 changed files with 14 additions and 5 deletions
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@ -2812,6 +2812,13 @@ static int double_lock_balance(struct rq *this_rq, struct rq *busiest)
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return ret;
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}
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static void double_unlock_balance(struct rq *this_rq, struct rq *busiest)
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__releases(busiest->lock)
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{
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spin_unlock(&busiest->lock);
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lock_set_subclass(&this_rq->lock.dep_map, 0, _RET_IP_);
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}
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/*
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* If dest_cpu is allowed for this process, migrate the task to it.
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* This is accomplished by forcing the cpu_allowed mask to only
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@ -3636,7 +3643,7 @@ load_balance_newidle(int this_cpu, struct rq *this_rq, struct sched_domain *sd,
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ld_moved = move_tasks(this_rq, this_cpu, busiest,
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imbalance, sd, CPU_NEWLY_IDLE,
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&all_pinned);
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spin_unlock(&busiest->lock);
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double_unlock_balance(this_rq, busiest);
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if (unlikely(all_pinned)) {
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cpu_clear(cpu_of(busiest), *cpus);
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@ -3751,7 +3758,7 @@ static void active_load_balance(struct rq *busiest_rq, int busiest_cpu)
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else
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schedstat_inc(sd, alb_failed);
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}
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spin_unlock(&target_rq->lock);
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double_unlock_balance(busiest_rq, target_rq);
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}
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#ifdef CONFIG_NO_HZ
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@ -861,6 +861,8 @@ static void put_prev_task_rt(struct rq *rq, struct task_struct *p)
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#define RT_MAX_TRIES 3
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static int double_lock_balance(struct rq *this_rq, struct rq *busiest);
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static void double_unlock_balance(struct rq *this_rq, struct rq *busiest);
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static void deactivate_task(struct rq *rq, struct task_struct *p, int sleep);
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static int pick_rt_task(struct rq *rq, struct task_struct *p, int cpu)
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@ -1022,7 +1024,7 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
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break;
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/* try again */
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spin_unlock(&lowest_rq->lock);
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double_unlock_balance(rq, lowest_rq);
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lowest_rq = NULL;
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}
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@ -1091,7 +1093,7 @@ static int push_rt_task(struct rq *rq)
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resched_task(lowest_rq->curr);
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spin_unlock(&lowest_rq->lock);
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double_unlock_balance(rq, lowest_rq);
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ret = 1;
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out:
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@ -1197,7 +1199,7 @@ static int pull_rt_task(struct rq *this_rq)
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}
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skip:
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spin_unlock(&src_rq->lock);
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double_unlock_balance(this_rq, src_rq);
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}
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return ret;
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