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rcu: Permit rt_mutex_unlock() with irqs disabled

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Create a separate lockdep class for the rt_mutex used for RCU priority
boosting and enable use of rt_mutex_lock() with irqs disabled.  This
prevents RCU priority boosting from falling prey to deadlocks when
someone begins an RCU read-side critical section in preemptible state,
but releases it with an irq-disabled lock held.

Unfortunately, the scheduler's runqueue and priority-inheritance locks
still must either completely enclose or be completely enclosed by any
overlapping RCU read-side critical section.

This version removes a redundant local_irq_restore() noted by
Yong Zhang.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2011-08-16 17:46:46 -07:00 committed by Paul E. McKenney
parent 06ae115a1d
commit 5342e269b2
2 changed files with 13 additions and 0 deletions
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5
kernel/rcutree_plugin.h
View file

@ -1149,6 +1149,8 @@ static void rcu_initiate_boost_trace(struct rcu_node *rnp)
#endif /* #else #ifdef CONFIG_RCU_TRACE */
static struct lock_class_key rcu_boost_class;
/*
* Carry out RCU priority boosting on the task indicated by ->exp_tasks
* or ->boost_tasks, advancing the pointer to the next task in the
@ -1211,6 +1213,9 @@ static int rcu_boost(struct rcu_node *rnp)
*/
t = container_of(tb, struct task_struct, rcu_node_entry);
rt_mutex_init_proxy_locked(&mtx, t);
/* Avoid lockdep false positives. This rt_mutex is its own thing. */
lockdep_set_class_and_name(&mtx.wait_lock, &rcu_boost_class,
"rcu_boost_mutex");
t->rcu_boost_mutex = &mtx;
raw_spin_unlock_irqrestore(&rnp->lock, flags);
rt_mutex_lock(&mtx); /* Side effect: boosts task t's priority. */

8
kernel/rtmutex.c
View file

@ -579,6 +579,7 @@ __rt_mutex_slowlock(struct rt_mutex *lock, int state,
struct rt_mutex_waiter *waiter)
{
int ret = 0;
int was_disabled;
for (;;) {
/* Try to acquire the lock: */
@ -601,10 +602,17 @@ __rt_mutex_slowlock(struct rt_mutex *lock, int state,
raw_spin_unlock(&lock->wait_lock);
was_disabled = irqs_disabled();
if (was_disabled)
local_irq_enable();
debug_rt_mutex_print_deadlock(waiter);
schedule_rt_mutex(lock);
if (was_disabled)
local_irq_disable();
raw_spin_lock(&lock->wait_lock);
set_current_state(state);
}