diff options
| -rw-r--r-- | include/linux/rcupdate.h | 26 | ||||
| -rw-r--r-- | kernel/rcupdate.c | 2 | ||||
| -rw-r--r-- | kernel/rcutiny.c | 1 | ||||
| -rw-r--r-- | kernel/rcutree.c | 1 |
4 files changed, 30 insertions, 0 deletions
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 8d315b013e37..bf91fcfe181c 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -228,6 +228,15 @@ static inline void destroy_rcu_head_on_stack(struct rcu_head *head) #ifdef CONFIG_DEBUG_LOCK_ALLOC +#ifdef CONFIG_PROVE_RCU +extern int rcu_is_cpu_idle(void); +#else /* !CONFIG_PROVE_RCU */ +static inline int rcu_is_cpu_idle(void) +{ + return 0; +} +#endif /* else !CONFIG_PROVE_RCU */ + extern struct lockdep_map rcu_lock_map; # define rcu_read_acquire() \ lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) @@ -262,6 +271,8 @@ static inline int rcu_read_lock_held(void) { if (!debug_lockdep_rcu_enabled()) return 1; + if (rcu_is_cpu_idle()) + return 0; return lock_is_held(&rcu_lock_map); } @@ -285,6 +296,19 @@ extern int rcu_read_lock_bh_held(void); * * 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. */ #ifdef CONFIG_PREEMPT_COUNT static inline int rcu_read_lock_sched_held(void) @@ -293,6 +317,8 @@ static inline int rcu_read_lock_sched_held(void) if (!debug_lockdep_rcu_enabled()) return 1; + if (rcu_is_cpu_idle()) + return 0; if (debug_locks) lockdep_opinion = lock_is_held(&rcu_sched_lock_map); return lockdep_opinion || preempt_count() != 0 || irqs_disabled(); diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c index 92e771d7b44b..2bc4e135ff23 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -93,6 +93,8 @@ int rcu_read_lock_bh_held(void) { if (!debug_lockdep_rcu_enabled()) return 1; + if (rcu_is_cpu_idle()) + return 0; return in_softirq() || irqs_disabled(); } EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held); diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c index 3ab77bdc90c4..b4e0b4981768 100644 --- a/kernel/rcutiny.c +++ b/kernel/rcutiny.c @@ -157,6 +157,7 @@ int rcu_is_cpu_idle(void) { return !rcu_dynticks_nesting; } +EXPORT_SYMBOL(rcu_is_cpu_idle); #endif /* #ifdef CONFIG_PROVE_RCU */ diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 8afb2e89745b..489b62a67d35 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -567,6 +567,7 @@ int rcu_is_cpu_idle(void) preempt_enable(); return ret; } +EXPORT_SYMBOL(rcu_is_cpu_idle); #endif /* #ifdef CONFIG_PROVE_RCU */ |