diff options
Diffstat (limited to 'kernel')
-rw-r--r-- | kernel/rcu/update.c | 49 |
1 files changed, 49 insertions, 0 deletions
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c index afaecb7a799a..fec5f48b8860 100644 --- a/kernel/rcu/update.c +++ b/kernel/rcu/update.c @@ -62,6 +62,55 @@ MODULE_ALIAS("rcupdate"); module_param(rcu_expedited, int, 0); +#if defined(CONFIG_DEBUG_LOCK_ALLOC) && defined(CONFIG_PREEMPT_COUNT) +/** + * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section? + * + * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an + * RCU-sched read-side critical section. In absence of + * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side + * critical section unless it can prove otherwise. Note that disabling + * of preemption (including disabling irqs) counts as an RCU-sched + * read-side critical section. This is useful for debug checks in functions + * that required that they be called within an RCU-sched read-side + * critical section. + * + * Check debug_lockdep_rcu_enabled() to prevent false positives during boot + * and while lockdep is disabled. + * + * Note that if the CPU is in the idle loop from an RCU point of + * view (ie: that we are in the section between rcu_idle_enter() and + * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU + * did an rcu_read_lock(). The reason for this is that RCU ignores CPUs + * that are in such a section, considering these as in extended quiescent + * state, so such a CPU is effectively never in an RCU read-side critical + * section regardless of what RCU primitives it invokes. This state of + * affairs is required --- we need to keep an RCU-free window in idle + * where the CPU may possibly enter into low power mode. This way we can + * notice an extended quiescent state to other CPUs that started a grace + * period. Otherwise we would delay any grace period as long as we run in + * the idle task. + * + * Similarly, we avoid claiming an SRCU read lock held if the current + * CPU is offline. + */ +int rcu_read_lock_sched_held(void) +{ + int lockdep_opinion = 0; + + if (!debug_lockdep_rcu_enabled()) + return 1; + if (!rcu_is_watching()) + return 0; + if (!rcu_lockdep_current_cpu_online()) + return 0; + if (debug_locks) + lockdep_opinion = lock_is_held(&rcu_sched_lock_map); + return lockdep_opinion || preempt_count() != 0 || irqs_disabled(); +} +EXPORT_SYMBOL(rcu_read_lock_sched_held); +#endif + #ifndef CONFIG_TINY_RCU static atomic_t rcu_expedited_nesting = |