From cc6783f788d8fe8b23ec6fc2762f5e8c9a418eee Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 6 Sep 2013 17:39:49 -0700 Subject: rcu: Is it safe to enter an RCU read-side critical section? There is currently no way for kernel code to determine whether it is safe to enter an RCU read-side critical section, in other words, whether or not RCU is paying attention to the currently running CPU. Given the large and increasing quantity of code shared by the idle loop and non-idle code, the this shortcoming is becoming increasingly painful. This commit therefore adds __rcu_is_watching(), which returns true if it is safe to enter an RCU read-side critical section on the currently running CPU. This function is quite fast, using only a __this_cpu_read(). However, the caller must disable preemption. Reported-by: Steven Rostedt Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutiny.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'kernel/rcutiny.c') diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c index 9ed6075dc562..b4bc61874d77 100644 --- a/kernel/rcutiny.c +++ b/kernel/rcutiny.c @@ -174,7 +174,7 @@ void rcu_irq_enter(void) } EXPORT_SYMBOL_GPL(rcu_irq_enter); -#ifdef CONFIG_DEBUG_LOCK_ALLOC +#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) /* * Test whether RCU thinks that the current CPU is idle. @@ -185,7 +185,7 @@ int rcu_is_cpu_idle(void) } EXPORT_SYMBOL(rcu_is_cpu_idle); -#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ +#endif /* defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) */ /* * Test whether the current CPU was interrupted from idle. Nested -- cgit v1.2.2 From 5c173eb8bcb9c1aa888bd6d14a4cb746f3dd2420 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 13 Sep 2013 17:20:11 -0700 Subject: rcu: Consistent rcu_is_watching() naming The old rcu_is_cpu_idle() function is just __rcu_is_watching() with preemption disabled. This commit therefore renames rcu_is_cpu_idle() to rcu_is_watching. Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutiny.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'kernel/rcutiny.c') diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c index b4bc61874d77..0fa061dfa55d 100644 --- a/kernel/rcutiny.c +++ b/kernel/rcutiny.c @@ -179,11 +179,11 @@ EXPORT_SYMBOL_GPL(rcu_irq_enter); /* * Test whether RCU thinks that the current CPU is idle. */ -int rcu_is_cpu_idle(void) +bool __rcu_is_watching(void) { - return !rcu_dynticks_nesting; + return rcu_dynticks_nesting; } -EXPORT_SYMBOL(rcu_is_cpu_idle); +EXPORT_SYMBOL(__rcu_is_watching); #endif /* defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) */ -- cgit v1.2.2