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| -rw-r--r-- | kern/spinlock.c | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/kern/spinlock.c b/kern/spinlock.c index aa49cffb..68e84215 100644 --- a/kern/spinlock.c +++ b/kern/spinlock.c @@ -51,6 +51,16 @@ * and fast paths operations fail. The lock operation must make sure * that the lock value is restored to SPINLOCK_LOCKED if there is no * more contention, an operation called downgrading. + * + * In order to enforce correct visibility of the critical section, + * acquire and release atomic operations are used when accessing a + * qnode lock. Similarly, acquire and release semantics are also used + * when accessing the lock word which stores the first and last QIDs, + * so that the memory operations on the qnodes referenced by those QIDs + * are correctly enforced. Accessing the next QID in a qnode however + * is performed with no memory order constraint, because the qnodes + * referenced by those QID are never accessed unless they are the first + * or the last, cases which do enforce ordering. */ #include <assert.h> |