From 3842a0832a1d6eb0b31421f8810a813135967512 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 28 Nov 2011 10:42:42 -0800 Subject: rcu: Document same-context read-side constraints The intent is that a given RCU read-side critical section be confined to a single context. For example, it is illegal to invoke rcu_read_lock() in an exception handler and then invoke rcu_read_unlock() from the context of the task that received the exception. Suggested-by: Peter Zijlstra Signed-off-by: Paul E. McKenney --- include/linux/rcupdate.h | 15 +++++++++++++++ 1 file changed, 15 insertions(+) (limited to 'include/linux/rcupdate.h') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 5dd6fd8b3203..81c04f4348ec 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -265,6 +265,11 @@ extern int debug_lockdep_rcu_enabled(void); * * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot * and while lockdep is disabled. + * + * Note that rcu_read_lock() and the matching rcu_read_unlock() must + * occur in the same context, for example, it is illegal to invoke + * rcu_read_unlock() in process context if the matching rcu_read_lock() + * was invoked from within an irq handler. */ static inline int rcu_read_lock_held(void) { @@ -689,6 +694,11 @@ static inline void rcu_read_unlock(void) * critical sections in interrupt context can use just rcu_read_lock(), * though this should at least be commented to avoid confusing people * reading the code. + * + * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh() + * must occur in the same context, for example, it is illegal to invoke + * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh() + * was invoked from some other task. */ static inline void rcu_read_lock_bh(void) { @@ -716,6 +726,11 @@ static inline void rcu_read_unlock_bh(void) * are being done using call_rcu_sched() or synchronize_rcu_sched(). * Read-side critical sections can also be introduced by anything that * disables preemption, including local_irq_disable() and friends. + * + * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched() + * must occur in the same context, for example, it is illegal to invoke + * rcu_read_unlock_sched() from process context if the matching + * rcu_read_lock_sched() was invoked from an NMI handler. */ static inline void rcu_read_lock_sched(void) { -- cgit v1.2.3