path: root/Documentation/RCU/whatisRCU.txt
diff options
Diffstat (limited to 'Documentation/RCU/whatisRCU.txt')
1 files changed, 22 insertions, 10 deletions
diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt
index 6bbe8dcdc3d..0cc7820967f 100644
--- a/Documentation/RCU/whatisRCU.txt
+++ b/Documentation/RCU/whatisRCU.txt
@@ -499,6 +499,8 @@ The foo_reclaim() function might appear as follows:
struct foo *fp = container_of(rp, struct foo, rcu);
+ foo_cleanup(fp->a);
@@ -521,6 +523,12 @@ o Use call_rcu() -after- removing a data element from an
read-side critical sections that might be referencing that
data item.
+If the callback for call_rcu() is not doing anything more than calling
+kfree() on the structure, you can use kfree_rcu() instead of call_rcu()
+to avoid having to write your own callback:
+ kfree_rcu(old_fp, rcu);
Again, see checklist.txt for additional rules governing the use of RCU.
@@ -773,8 +781,8 @@ a single atomic update, converting to RCU will require special care.
Also, the presence of synchronize_rcu() means that the RCU version of
delete() can now block. If this is a problem, there is a callback-based
-mechanism that never blocks, namely call_rcu(), that can be used in
-place of synchronize_rcu().
+mechanism that never blocks, namely call_rcu() or kfree_rcu(), that can
+be used in place of synchronize_rcu().
@@ -789,9 +797,7 @@ RCU list traversal:
- list_for_each_continue_rcu (to be deprecated in favor of new
- list_for_each_entry_continue_rcu)
+ list_for_each_entry_continue_rcu
RCU pointer/list update:
@@ -813,6 +819,7 @@ RCU: Critical sections Grace period Barrier
rcu_read_unlock synchronize_rcu
rcu_dereference synchronize_rcu_expedited
+ kfree_rcu
bh: Critical sections Grace period Barrier
@@ -833,9 +840,9 @@ sched: Critical sections Grace period Barrier
SRCU: Critical sections Grace period Barrier
- srcu_read_lock synchronize_srcu N/A
- srcu_read_unlock synchronize_srcu_expedited
- srcu_read_lock_raw
+ srcu_read_lock synchronize_srcu srcu_barrier
+ srcu_read_unlock call_srcu
+ srcu_read_lock_raw synchronize_srcu_expedited
@@ -873,7 +880,7 @@ d. Do you need to treat NMI handlers, hardirq handlers,
and code segments with preemption disabled (whether
via preempt_disable(), local_irq_save(), local_bh_disable(),
or some other mechanism) as if they were explicit RCU readers?
- If so, you need RCU-sched.
+ If so, RCU-sched is the only choice that will work for you.
e. Do you need RCU grace periods to complete even in the face
of softirq monopolization of one or more of the CPUs? For
@@ -884,7 +891,12 @@ f. Is your workload too update-intensive for normal use of
RCU, but inappropriate for other synchronization mechanisms?
If so, consider SLAB_DESTROY_BY_RCU. But please be careful!
-g. Otherwise, use RCU.
+g. Do you need read-side critical sections that are respected
+ even though they are in the middle of the idle loop, during
+ user-mode execution, or on an offlined CPU? If so, SRCU is the
+ only choice that will work for you.
+h. Otherwise, use RCU.
Of course, this all assumes that you have determined that RCU is in fact
the right tool for your job.