patch-2_6_7-vs1_9_1_12

[linux-2.6.git] / lib / rwsem.c

diff --git a/lib/rwsem.c b/lib/rwsem.c
index ce15eb0..27dcd95 100644 (file)
--- a/lib/rwsem.c
+++ b/lib/rwsem.c
@@ -29,15 +29,15 @@ void rwsemtrace(struct rw_semaphore *sem, const char *str)
 
 /*
  * handle the lock being released whilst there are processes blocked on it that can now run
- * - if we come here, then:
- *   - the 'active part' of the count (&0x0000ffff) reached zero but has been re-incremented
+ * - if we come here from up_xxxx(), then:
+ *   - the 'active part' of the count (&0x0000ffff) had reached zero (but may have changed)
  *   - the 'waiting part' of the count (&0xffff0000) is negative (and will still be so)
  *   - there must be someone on the queue
  * - the spinlock must be held by the caller
  * - woken process blocks are discarded from the list after having task zeroed
- * - writers are only woken if wakewrite is non-zero
+ * - writers are only woken if downgrading is false
  */
-static inline struct rw_semaphore *__rwsem_do_wake(struct rw_semaphore *sem, int wakewrite)
+static inline struct rw_semaphore *__rwsem_do_wake(struct rw_semaphore *sem, int downgrading)
 {
        struct rwsem_waiter *waiter;
        struct task_struct *tsk;
@@ -46,10 +46,12 @@ static inline struct rw_semaphore *__rwsem_do_wake(struct rw_semaphore *sem, int
 
        rwsemtrace(sem,"Entering __rwsem_do_wake");
 
-       if (!wakewrite)
+       if (downgrading)
                goto dont_wake_writers;
 
-       /* only wake someone up if we can transition the active part of the count from 0 -> 1 */
+       /* if we came through an up_xxxx() call, we only only wake someone up
+        * if we can transition the active part of the count from 0 -> 1
+        */
  try_again:
        oldcount = rwsem_atomic_update(RWSEM_ACTIVE_BIAS,sem) - RWSEM_ACTIVE_BIAS;
        if (oldcount & RWSEM_ACTIVE_MASK)
@@ -78,9 +80,10 @@ static inline struct rw_semaphore *__rwsem_do_wake(struct rw_semaphore *sem, int
        if (waiter->flags & RWSEM_WAITING_FOR_WRITE)
                goto out;
 
-       /* grant an infinite number of read locks to the readers at the front of the queue
-        * - note we increment the 'active part' of the count by the number of readers (less one
-        *   for the activity decrement we've already done) before waking any processes up
+       /* grant an infinite number of read locks to the readers at the front
+        * of the queue
+        * - note we increment the 'active part' of the count by the number of
+        *   readers before waking any processes up
         */
  readers_only:
        woken = 0;
@@ -95,8 +98,10 @@ static inline struct rw_semaphore *__rwsem_do_wake(struct rw_semaphore *sem, int
        } while (waiter->flags & RWSEM_WAITING_FOR_READ);
 
        loop = woken;
-       woken *= RWSEM_ACTIVE_BIAS-RWSEM_WAITING_BIAS;
-       woken -= RWSEM_ACTIVE_BIAS;
+       woken *= RWSEM_ACTIVE_BIAS - RWSEM_WAITING_BIAS;
+       if (!downgrading)
+               woken -= RWSEM_ACTIVE_BIAS; /* we'd already done one increment
+                                            * earlier */
        rwsem_atomic_add(woken,sem);
 
        next = sem->wait_list.next;
@@ -150,7 +155,7 @@ static inline struct rw_semaphore *rwsem_down_failed_common(struct rw_semaphore
         * - it might even be this process, since the waker takes a more active part
         */
        if (!(count & RWSEM_ACTIVE_MASK))
-               sem = __rwsem_do_wake(sem,1);
+               sem = __rwsem_do_wake(sem, 0);
 
        spin_unlock(&sem->wait_lock);
 
@@ -201,7 +206,7 @@ struct rw_semaphore fastcall __sched *rwsem_down_write_failed(struct rw_semaphor
 
 /*
  * handle waking up a waiter on the semaphore
- * - up_read has decremented the active part of the count if we come here
+ * - up_read/up_write has decremented the active part of the count if we come here
  */
 struct rw_semaphore fastcall *rwsem_wake(struct rw_semaphore *sem)
 {
@@ -211,7 +216,7 @@ struct rw_semaphore fastcall *rwsem_wake(struct rw_semaphore *sem)
 
        /* do nothing if list empty */
        if (!list_empty(&sem->wait_list))
-               sem = __rwsem_do_wake(sem,1);
+               sem = __rwsem_do_wake(sem, 0);
 
        spin_unlock(&sem->wait_lock);
 
@@ -233,7 +238,7 @@ struct rw_semaphore fastcall *rwsem_downgrade_wake(struct rw_semaphore *sem)
 
        /* do nothing if list empty */
        if (!list_empty(&sem->wait_list))
-               sem = __rwsem_do_wake(sem,0);
+               sem = __rwsem_do_wake(sem, 1);
 
        spin_unlock(&sem->wait_lock);