diff options
Diffstat (limited to 'Documentation/RCU/checklist.rst')
| -rw-r--r-- | Documentation/RCU/checklist.rst | 17 |
1 files changed, 11 insertions, 6 deletions
diff --git a/Documentation/RCU/checklist.rst b/Documentation/RCU/checklist.rst index 2efed9926c3f..1030119294d0 100644 --- a/Documentation/RCU/checklist.rst +++ b/Documentation/RCU/checklist.rst @@ -70,7 +70,7 @@ over a rather long period of time, but improvements are always welcome! is less readable and prevents lockdep from detecting locking issues. Letting RCU-protected pointers "leak" out of an RCU read-side - critical section is every bid as bad as letting them leak out + critical section is every bit as bad as letting them leak out from under a lock. Unless, of course, you have arranged some other means of protection, such as a lock or a reference count -before- letting them out of the RCU read-side critical section. @@ -129,9 +129,7 @@ over a rather long period of time, but improvements are always welcome! accesses. The rcu_dereference() primitive ensures that the CPU picks up the pointer before it picks up the data that the pointer points to. This really is necessary - on Alpha CPUs. If you don't believe me, see: - - http://www.openvms.compaq.com/wizard/wiz_2637.html + on Alpha CPUs. The rcu_dereference() primitive is also an excellent documentation aid, letting the person reading the @@ -214,9 +212,9 @@ over a rather long period of time, but improvements are always welcome! the rest of the system. 7. As of v4.20, a given kernel implements only one RCU flavor, - which is RCU-sched for PREEMPT=n and RCU-preempt for PREEMPT=y. + which is RCU-sched for PREEMPTION=n and RCU-preempt for PREEMPTION=y. If the updater uses call_rcu() or synchronize_rcu(), - then the corresponding readers my use rcu_read_lock() and + then the corresponding readers may use rcu_read_lock() and rcu_read_unlock(), rcu_read_lock_bh() and rcu_read_unlock_bh(), or any pair of primitives that disables and re-enables preemption, for example, rcu_read_lock_sched() and rcu_read_unlock_sched(). @@ -314,6 +312,13 @@ over a rather long period of time, but improvements are always welcome! shared between readers and updaters. Additional primitives are provided for this case, as discussed in lockdep.txt. + One exception to this rule is when data is only ever added to + the linked data structure, and is never removed during any + time that readers might be accessing that structure. In such + cases, READ_ONCE() may be used in place of rcu_dereference() + and the read-side markers (rcu_read_lock() and rcu_read_unlock(), + for example) may be omitted. + 10. Conversely, if you are in an RCU read-side critical section, and you don't hold the appropriate update-side lock, you -must- use the "_rcu()" variants of the list macros. Failing to do so |