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rcu: Document same-context read-side constraints

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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 <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2011-11-28 10:42:42 -08:00
parent f0e7c19db8
commit 3842a0832a
2 changed files with 20 additions and 0 deletions
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15
include/linux/rcupdate.h
View file

@ -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)
{

5
include/linux/srcu.h
View file

@ -158,6 +158,11 @@ static inline int srcu_read_lock_held(struct srcu_struct *sp)
* one way to indirectly wait on an SRCU grace period is to acquire
* a mutex that is held elsewhere while calling synchronize_srcu() or
* synchronize_srcu_expedited().
*
* Note that srcu_read_lock() and the matching srcu_read_unlock() must
* occur in the same context, for example, it is illegal to invoke
* srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
* was invoked in process context.
*/
static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
{