diff options
Diffstat (limited to 'Documentation/RCU/checklist.txt')
| -rw-r--r-- | Documentation/RCU/checklist.txt | 39 |
1 files changed, 20 insertions, 19 deletions
diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt index 5c8d74968090..fc103d7a0474 100644 --- a/Documentation/RCU/checklist.txt +++ b/Documentation/RCU/checklist.txt @@ -162,9 +162,9 @@ over a rather long period of time, but improvements are always welcome! when publicizing a pointer to a structure that can be traversed by an RCU read-side critical section. -5. If call_rcu(), or a related primitive such as call_rcu_bh() or - call_rcu_sched(), is used, the callback function must be - written to be called from softirq context. In particular, +5. If call_rcu(), or a related primitive such as call_rcu_bh(), + call_rcu_sched(), or call_srcu() is used, the callback function + must be written to be called from softirq context. In particular, it cannot block. 6. Since synchronize_rcu() can block, it cannot be called from @@ -202,11 +202,12 @@ over a rather long period of time, but improvements are always welcome! updater uses call_rcu_sched() or synchronize_sched(), then the corresponding readers must disable preemption, possibly by calling rcu_read_lock_sched() and rcu_read_unlock_sched(). - If the updater uses synchronize_srcu(), the the corresponding - readers must use srcu_read_lock() and srcu_read_unlock(), - and with the same srcu_struct. The rules for the expedited - primitives are the same as for their non-expedited counterparts. - Mixing things up will result in confusion and broken kernels. + If the updater uses synchronize_srcu() or call_srcu(), + the the corresponding readers must use srcu_read_lock() and + srcu_read_unlock(), and with the same srcu_struct. The rules for + the expedited primitives are the same as for their non-expedited + counterparts. Mixing things up will result in confusion and + broken kernels. One exception to this rule: rcu_read_lock() and rcu_read_unlock() may be substituted for rcu_read_lock_bh() and rcu_read_unlock_bh() @@ -333,14 +334,14 @@ over a rather long period of time, but improvements are always welcome! victim CPU from ever going offline.) 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. + synchronize_srcu(), synchronize_srcu_expedited(), and call_srcu()) + 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. If you need to enter your read-side critical section in a hardirq or exception handler, and then exit that same read-side @@ -353,8 +354,8 @@ over a rather long period of time, but improvements are always welcome! cleanup_srcu_struct(). These are passed a "struct srcu_struct" that defines the scope of a given SRCU domain. Once initialized, the srcu_struct is passed to srcu_read_lock(), srcu_read_unlock() - synchronize_srcu(), and synchronize_srcu_expedited(). A given - synchronize_srcu() waits only for SRCU read-side critical + synchronize_srcu(), synchronize_srcu_expedited(), and call_srcu(). + A given synchronize_srcu() waits only for SRCU read-side critical sections governed by srcu_read_lock() and srcu_read_unlock() calls that have been passed the same srcu_struct. This property is what makes sleeping read-side critical sections tolerable -- @@ -374,7 +375,7 @@ over a rather long period of time, but improvements are always welcome! requiring SRCU's read-side deadlock immunity or low read-side realtime latency. - Note that, rcu_assign_pointer() relates to SRCU just as they do + Note that, rcu_assign_pointer() relates to SRCU just as it does to other forms of RCU. 15. The whole point of call_rcu(), synchronize_rcu(), and friends |