+Please note that the "What is RCU?" LWN series is an excellent place
+to start learning about RCU:
+
+1. What is RCU, Fundamentally? http://lwn.net/Articles/262464/
+2. What is RCU? Part 2: Usage http://lwn.net/Articles/263130/
+3. RCU part 3: the RCU API http://lwn.net/Articles/264090/
+
+
What is RCU?
RCU is a synchronization mechanism that was added to the Linux kernel
and release a global reader-writer lock. The synchronize_rcu()
primitive write-acquires this same lock, then immediately releases
it. This means that once synchronize_rcu() exits, all RCU read-side
-critical sections that were in progress before synchonize_rcu() was
+critical sections that were in progress before synchronize_rcu() was
called are guaranteed to have completed -- there is no way that
synchronize_rcu() would have been able to write-acquire the lock
otherwise.
Either way, the differences are quite small. Read-side locking moves
to rcu_read_lock() and rcu_read_unlock, update-side locking moves from
-from a reader-writer lock to a simple spinlock, and a synchronize_rcu()
+a reader-writer lock to a simple spinlock, and a synchronize_rcu()
precedes the kfree().
However, there is one potential catch: the read-side and update-side
APIs, since there does not appear to be a way to categorize them
in docbook. Here is the list, by category.
-Markers for RCU read-side critical sections:
-
- rcu_read_lock
- rcu_read_unlock
- rcu_read_lock_bh
- rcu_read_unlock_bh
-
RCU pointer/list traversal:
rcu_dereference
+ list_for_each_entry_rcu
+ hlist_for_each_entry_rcu
+
list_for_each_rcu (to be deprecated in favor of
list_for_each_entry_rcu)
- list_for_each_entry_rcu
list_for_each_continue_rcu (to be deprecated in favor of new
list_for_each_entry_continue_rcu)
- hlist_for_each_entry_rcu
-RCU pointer update:
+RCU pointer/list update:
rcu_assign_pointer
list_add_rcu
list_del_rcu
list_replace_rcu
hlist_del_rcu
+ hlist_add_after_rcu
+ hlist_add_before_rcu
hlist_add_head_rcu
+ hlist_replace_rcu
+ list_splice_init_rcu()
+
+RCU: Critical sections Grace period Barrier
+
+ rcu_read_lock synchronize_net rcu_barrier
+ rcu_read_unlock synchronize_rcu
+ call_rcu
+
+
+bh: Critical sections Grace period Barrier
+
+ rcu_read_lock_bh call_rcu_bh rcu_barrier_bh
+ rcu_read_unlock_bh
+
+
+sched: Critical sections Grace period Barrier
+
+ [preempt_disable] synchronize_sched rcu_barrier_sched
+ [and friends] call_rcu_sched
+
+
+SRCU: Critical sections Grace period Barrier
-RCU grace period:
+ srcu_read_lock synchronize_srcu N/A
+ srcu_read_unlock
- synchronize_net
- synchronize_sched
- synchronize_rcu
- call_rcu
- call_rcu_bh
See the comment headers in the source code (or the docbook generated
from them) for more information.