diff options
Diffstat (limited to 'Documentation/RCU/whatisRCU.txt')
| -rw-r--r-- | Documentation/RCU/whatisRCU.txt | 18 |
1 files changed, 14 insertions, 4 deletions
diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt index 07cb93b82ba9..318df44259b3 100644 --- a/Documentation/RCU/whatisRCU.txt +++ b/Documentation/RCU/whatisRCU.txt @@ -184,7 +184,17 @@ synchronize_rcu() blocking, it registers a function and argument which are invoked after all ongoing RCU read-side critical sections have completed. This callback variant is particularly useful in situations where - it is illegal to block. + it is illegal to block or where update-side performance is + critically important. + + However, the call_rcu() API should not be used lightly, as use + of the synchronize_rcu() API generally results in simpler code. + In addition, the synchronize_rcu() API has the nice property + of automatically limiting update rate should grace periods + be delayed. This property results in system resilience in face + of denial-of-service attacks. Code using call_rcu() should limit + update rate in order to gain this same sort of resilience. See + checklist.txt for some approaches to limiting the update rate. rcu_assign_pointer() @@ -677,8 +687,9 @@ diff shows how closely related RCU and reader-writer locking can be. + spin_lock(&listmutex); list_for_each_entry(p, head, lp) { if (p->key == key) { - list_del(&p->list); + - list_del(&p->list); - write_unlock(&listmutex); + + list_del_rcu(&p->list); + spin_unlock(&listmutex); + synchronize_rcu(); kfree(p); @@ -726,7 +737,7 @@ Or, for those who prefer a side-by-side listing: 5 write_lock(&listmutex); 5 spin_lock(&listmutex); 6 list_for_each_entry(p, head, lp) { 6 list_for_each_entry(p, head, lp) { 7 if (p->key == key) { 7 if (p->key == key) { - 8 list_del(&p->list); 8 list_del(&p->list); + 8 list_del(&p->list); 8 list_del_rcu(&p->list); 9 write_unlock(&listmutex); 9 spin_unlock(&listmutex); 10 synchronize_rcu(); 10 kfree(p); 11 kfree(p); @@ -790,7 +801,6 @@ RCU pointer update: RCU grace period: - synchronize_kernel (deprecated) synchronize_net synchronize_sched synchronize_rcu |