diff options
| -rw-r--r-- | include/linux/rwsem.h | 17 |
1 files changed, 15 insertions, 2 deletions
diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h index 658afb37c3f5..7b524b4109a0 100644 --- a/include/linux/rwsem.h +++ b/include/linux/rwsem.h @@ -61,12 +61,25 @@ extern void downgrade_write(struct rw_semaphore *sem); #ifdef CONFIG_DEBUG_LOCK_ALLOC /* - * nested locking: + * nested locking. NOTE: rwsems are not allowed to recurse + * (which occurs if the same task tries to acquire the same + * lock instance multiple times), but multiple locks of the + * same lock class might be taken, if the order of the locks + * is always the same. This ordering rule can be expressed + * to lockdep via the _nested() APIs, but enumerating the + * subclasses that are used. (If the nesting relationship is + * static then another method for expressing nested locking is + * the explicit definition of lock class keys and the use of + * lockdep_set_class() at lock initialization time. + * See Documentation/lockdep-design.txt for more details.) */ extern void down_read_nested(struct rw_semaphore *sem, int subclass); extern void down_write_nested(struct rw_semaphore *sem, int subclass); /* - * Take/release a lock when not the owner will release it: + * Take/release a lock when not the owner will release it. + * + * [ This API should be avoided as much as possible - the + * proper abstraction for this case is completions. ] */ extern void down_read_non_owner(struct rw_semaphore *sem); extern void up_read_non_owner(struct rw_semaphore *sem); |