diff options
| -rw-r--r-- | include/linux/rcupdate.h | 33 |
1 files changed, 6 insertions, 27 deletions
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index f0eecb9e49c8..d9680b798b21 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -702,33 +702,12 @@ static __always_inline void rcu_read_lock(void) /** * rcu_read_unlock() - marks the end of an RCU read-side critical section. * - * In most situations, rcu_read_unlock() is immune from deadlock. - * However, in kernels built with CONFIG_RCU_BOOST, rcu_read_unlock() - * is responsible for deboosting, which it does via rt_mutex_unlock(). - * Unfortunately, this function acquires the scheduler's runqueue and - * priority-inheritance spinlocks. This means that deadlock could result - * if the caller of rcu_read_unlock() already holds one of these locks or - * any lock that is ever acquired while holding them. - * - * That said, RCU readers are never priority boosted unless they were - * preempted. Therefore, one way to avoid deadlock is to make sure - * that preemption never happens within any RCU read-side critical - * section whose outermost rcu_read_unlock() is called with one of - * rt_mutex_unlock()'s locks held. Such preemption can be avoided in - * a number of ways, for example, by invoking preempt_disable() before - * critical section's outermost rcu_read_lock(). - * - * Given that the set of locks acquired by rt_mutex_unlock() might change - * at any time, a somewhat more future-proofed approach is to make sure - * that that preemption never happens within any RCU read-side critical - * section whose outermost rcu_read_unlock() is called with irqs disabled. - * This approach relies on the fact that rt_mutex_unlock() currently only - * acquires irq-disabled locks. - * - * The second of these two approaches is best in most situations, - * however, the first approach can also be useful, at least to those - * developers willing to keep abreast of the set of locks acquired by - * rt_mutex_unlock(). + * In almost all situations, rcu_read_unlock() is immune from deadlock. + * In recent kernels that have consolidated synchronize_sched() and + * synchronize_rcu_bh() into synchronize_rcu(), this deadlock immunity + * also extends to the scheduler's runqueue and priority-inheritance + * spinlocks, courtesy of the quiescent-state deferral that is carried + * out when rcu_read_unlock() is invoked with interrupts disabled. * * See rcu_read_lock() for more information. */ |