diff options
Diffstat (limited to 'Documentation/RCU/checklist.txt')
| -rw-r--r-- | Documentation/RCU/checklist.txt | 34 |
1 files changed, 20 insertions, 14 deletions
diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt index 767cf06a427..cbc180f9019 100644 --- a/Documentation/RCU/checklist.txt +++ b/Documentation/RCU/checklist.txt @@ -127,10 +127,14 @@ over a rather long period of time, but improvements are always welcome! perfectly legal (if redundant) for update-side code to use rcu_dereference() and the "_rcu()" list-traversal primitives. This is particularly useful in code that - is common to readers and updaters. However, neither - rcu_dereference() nor the "_rcu()" list-traversal - primitives can substitute for a good concurrency design - coordinating among multiple updaters. + is common to readers and updaters. However, lockdep + will complain if you access rcu_dereference() outside + of an RCU read-side critical section. See lockdep.txt + to learn what to do about this. + + Of course, neither rcu_dereference() nor the "_rcu()" + list-traversal primitives can substitute for a good + concurrency design coordinating among multiple updaters. b. If the list macros are being used, the list_add_tail_rcu() and list_add_rcu() primitives must be used in order @@ -249,7 +253,9 @@ over a rather long period of time, but improvements are always welcome! must be protected by appropriate update-side locks. RCU read-side critical sections are delimited by rcu_read_lock() and rcu_read_unlock(), or by similar primitives such as - rcu_read_lock_bh() and rcu_read_unlock_bh(). + rcu_read_lock_bh() and rcu_read_unlock_bh(), in which case + the matching rcu_dereference() primitive must be used in order + to keep lockdep happy, in this case, rcu_dereference_bh(). The reason that it is permissible to use RCU list-traversal primitives when the update-side lock is held is that doing so @@ -302,15 +308,15 @@ over a rather long period of time, but improvements are always welcome! not the case, a self-spawning RCU callback would prevent the victim CPU from ever going offline.) -14. SRCU (srcu_read_lock(), srcu_read_unlock(), synchronize_srcu(), - and synchronize_srcu_expedited()) may only be invoked from - process context. Unlike other forms of RCU, it -is- permissible - to block in an SRCU read-side critical section (demarked by - srcu_read_lock() and srcu_read_unlock()), hence the "SRCU": - "sleepable RCU". Please note that if you don't need to sleep - in read-side critical sections, you should be using RCU rather - than SRCU, because RCU is almost always faster and easier to - use than is SRCU. +14. SRCU (srcu_read_lock(), srcu_read_unlock(), srcu_dereference(), + synchronize_srcu(), and synchronize_srcu_expedited()) may only + be invoked from process context. Unlike other forms of RCU, it + -is- permissible to block in an SRCU read-side critical section + (demarked by srcu_read_lock() and srcu_read_unlock()), hence the + "SRCU": "sleepable RCU". Please note that if you don't need + to sleep in read-side critical sections, you should be using + RCU rather than SRCU, because RCU is almost always faster and + easier to use than is SRCU. Also unlike other forms of RCU, explicit initialization and cleanup is required via init_srcu_struct() and |