diff options
Diffstat (limited to 'Documentation/RCU/whatisRCU.txt')
| -rw-r--r-- | Documentation/RCU/whatisRCU.txt | 16 |
1 files changed, 10 insertions, 6 deletions
diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt index 65eb856526b7..94288f1b8759 100644 --- a/Documentation/RCU/whatisRCU.txt +++ b/Documentation/RCU/whatisRCU.txt @@ -588,6 +588,7 @@ It is extremely simple: void synchronize_rcu(void) { write_lock(&rcu_gp_mutex); + smp_mb__after_spinlock(); write_unlock(&rcu_gp_mutex); } @@ -609,12 +610,15 @@ don't forget about them when submitting patches making use of RCU!] The rcu_read_lock() and rcu_read_unlock() primitive read-acquire and release a global reader-writer lock. The synchronize_rcu() -primitive write-acquires this same lock, then immediately releases -it. This means that once synchronize_rcu() exits, all RCU read-side -critical sections that were in progress before synchronize_rcu() was -called are guaranteed to have completed -- there is no way that -synchronize_rcu() would have been able to write-acquire the lock -otherwise. +primitive write-acquires this same lock, then releases it. This means +that once synchronize_rcu() exits, all RCU read-side critical sections +that were in progress before synchronize_rcu() was called are guaranteed +to have completed -- there is no way that synchronize_rcu() would have +been able to write-acquire the lock otherwise. The smp_mb__after_spinlock() +promotes synchronize_rcu() to a full memory barrier in compliance with +the "Memory-Barrier Guarantees" listed in: + + Documentation/RCU/Design/Requirements/Requirements.html. It is possible to nest rcu_read_lock(), since reader-writer locks may be recursively acquired. Note also that rcu_read_lock() is immune |