diff options
Diffstat (limited to 'include/linux/rcupdate.h')
| -rw-r--r-- | include/linux/rcupdate.h | 91 |
1 files changed, 46 insertions, 45 deletions
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 5a75d19aa661..d231aa17b1d7 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -44,7 +44,6 @@ #include <linux/debugobjects.h> #include <linux/bug.h> #include <linux/compiler.h> -#include <linux/percpu.h> #include <asm/barrier.h> extern int rcu_expedited; /* for sysctl */ @@ -300,41 +299,6 @@ bool __rcu_is_watching(void); #endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP) */ /* - * Hooks for cond_resched() and friends to avoid RCU CPU stall warnings. - */ - -#define RCU_COND_RESCHED_LIM 256 /* ms vs. 100s of ms. */ -DECLARE_PER_CPU(int, rcu_cond_resched_count); -void rcu_resched(void); - -/* - * Is it time to report RCU quiescent states? - * - * Note unsynchronized access to rcu_cond_resched_count. Yes, we might - * increment some random CPU's count, and possibly also load the result from - * yet another CPU's count. We might even clobber some other CPU's attempt - * to zero its counter. This is all OK because the goal is not precision, - * but rather reasonable amortization of rcu_note_context_switch() overhead - * and extremely high probability of avoiding RCU CPU stall warnings. - * Note that this function has to be preempted in just the wrong place, - * many thousands of times in a row, for anything bad to happen. - */ -static inline bool rcu_should_resched(void) -{ - return raw_cpu_inc_return(rcu_cond_resched_count) >= - RCU_COND_RESCHED_LIM; -} - -/* - * Report quiscent states to RCU if it is time to do so. - */ -static inline void rcu_cond_resched(void) -{ - if (unlikely(rcu_should_resched())) - rcu_resched(); -} - -/* * Infrastructure to implement the synchronize_() primitives in * TREE_RCU and rcu_barrier_() primitives in TINY_RCU. */ @@ -358,9 +322,19 @@ void wait_rcu_gp(call_rcu_func_t crf); * initialization. */ #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD +void init_rcu_head(struct rcu_head *head); +void destroy_rcu_head(struct rcu_head *head); void init_rcu_head_on_stack(struct rcu_head *head); void destroy_rcu_head_on_stack(struct rcu_head *head); #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ +static inline void init_rcu_head(struct rcu_head *head) +{ +} + +static inline void destroy_rcu_head(struct rcu_head *head) +{ +} + static inline void init_rcu_head_on_stack(struct rcu_head *head) { } @@ -852,15 +826,14 @@ static inline void rcu_preempt_sleep_check(void) * read-side critical section that would block in a !PREEMPT kernel. * But if you want the full story, read on! * - * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), it - * is illegal to block while in an RCU read-side critical section. In - * preemptible RCU implementations (TREE_PREEMPT_RCU and TINY_PREEMPT_RCU) - * in CONFIG_PREEMPT kernel builds, RCU read-side critical sections may - * be preempted, but explicit blocking is illegal. Finally, in preemptible - * RCU implementations in real-time (with -rt patchset) kernel builds, - * RCU read-side critical sections may be preempted and they may also - * block, but only when acquiring spinlocks that are subject to priority - * inheritance. + * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), + * it is illegal to block while in an RCU read-side critical section. + * In preemptible RCU implementations (TREE_PREEMPT_RCU) in CONFIG_PREEMPT + * kernel builds, RCU read-side critical sections may be preempted, + * but explicit blocking is illegal. Finally, in preemptible RCU + * implementations in real-time (with -rt patchset) kernel builds, RCU + * read-side critical sections may be preempted and they may also block, but + * only when acquiring spinlocks that are subject to priority inheritance. */ static inline void rcu_read_lock(void) { @@ -884,6 +857,34 @@ static 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(). + * * See rcu_read_lock() for more information. */ static inline void rcu_read_unlock(void) |