1 files changed, 41 insertions, 51 deletions

diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index 447e08de1fab..2337b4bb2366 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -121,16 +121,19 @@ enum rwsem_wake_type {
  * - woken process blocks are discarded from the list after having task zeroed
  * - writers are only marked woken if downgrading is false
  */
-static struct rw_semaphore *
-__rwsem_mark_wake(struct rw_semaphore *sem,
-                  enum rwsem_wake_type wake_type, struct wake_q_head *wake_q)
+static void __rwsem_mark_wake(struct rw_semaphore *sem,
+                              enum rwsem_wake_type wake_type,
+                              struct wake_q_head *wake_q)
 {
-        struct rwsem_waiter *waiter;
-        struct task_struct *tsk;
-        struct list_head *next;
-        long oldcount, woken, loop, adjustment;
+        struct rwsem_waiter *waiter, *tmp;
+        long oldcount, woken = 0, adjustment = 0;
+
+        /*
+         * Take a peek at the queue head waiter such that we can determine
+         * the wakeup(s) to perform.
+         */
+        waiter = list_first_entry(&sem->wait_list, struct rwsem_waiter, list);
 
-        waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
         if (waiter->type == RWSEM_WAITING_FOR_WRITE) {
                 if (wake_type == RWSEM_WAKE_ANY) {
                         /*
@@ -142,19 +145,19 @@ __rwsem_mark_wake(struct rw_semaphore *sem,
                          */
                         wake_q_add(wake_q, waiter->task);
                 }
-                goto out;
+
+                return;
         }
 
-        /* Writers might steal the lock before we grant it to the next reader.
+        /*
+         * Writers might steal the lock before we grant it to the next reader.
          * We prefer to do the first reader grant before counting readers
          * so we can bail out early if a writer stole the lock.
          */
-        adjustment = 0;
         if (wake_type != RWSEM_WAKE_READ_OWNED) {
                 adjustment = RWSEM_ACTIVE_READ_BIAS;
  try_reader_grant:
                 oldcount = atomic_long_fetch_add(adjustment, &sem->count);
-
                 if (unlikely(oldcount < RWSEM_WAITING_BIAS)) {
                         /*
                          * If the count is still less than RWSEM_WAITING_BIAS
@@ -164,7 +167,8 @@ __rwsem_mark_wake(struct rw_semaphore *sem,
                          */
                         if (atomic_long_add_return(-adjustment, &sem->count) <
                             RWSEM_WAITING_BIAS)
-                                goto out;
+                                return;
+
                         /* Last active locker left. Retry waking readers. */
                         goto try_reader_grant;
                 }
@@ -176,38 +180,23 @@ __rwsem_mark_wake(struct rw_semaphore *sem,
                 rwsem_set_reader_owned(sem);
         }
 
-        /* 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.
+        /*
+         * Grant an infinite number of read locks to the readers at the front
+         * of the queue. We know that woken will be at least 1 as we accounted
+         * for above. Note we increment the 'active part' of the count by the
+         * number of readers before waking any processes up.
          */
-        woken = 0;
-        do {
-                woken++;
+        list_for_each_entry_safe(waiter, tmp, &sem->wait_list, list) {
+                struct task_struct *tsk;
 
-                if (waiter->list.next == &sem->wait_list)
+                if (waiter->type == RWSEM_WAITING_FOR_WRITE)
                         break;
 
-                waiter = list_entry(waiter->list.next,
-                                        struct rwsem_waiter, list);
-
-        } while (waiter->type != RWSEM_WAITING_FOR_WRITE);
-
-        adjustment = woken * RWSEM_ACTIVE_READ_BIAS - adjustment;
-        if (waiter->type != RWSEM_WAITING_FOR_WRITE)
-                /* hit end of list above */
-                adjustment -= RWSEM_WAITING_BIAS;
-
-        if (adjustment)
-                atomic_long_add(adjustment, &sem->count);
-
-        next = sem->wait_list.next;
-        loop = woken;
-        do {
-                waiter = list_entry(next, struct rwsem_waiter, list);
-                next = waiter->list.next;
+                woken++;
                 tsk = waiter->task;
 
                 wake_q_add(wake_q, tsk);
+                list_del(&waiter->list);
                 /*
                  * Ensure that the last operation is setting the reader
                  * waiter to nil such that rwsem_down_read_failed() cannot
@@ -215,13 +204,16 @@ __rwsem_mark_wake(struct rw_semaphore *sem,
                  * to the task to wakeup.
                  */
                 smp_store_release(&waiter->task, NULL);
-        } while (--loop);
+        }
 
-        sem->wait_list.next = next;
-        next->prev = &sem->wait_list;
+        adjustment = woken * RWSEM_ACTIVE_READ_BIAS - adjustment;
+        if (list_empty(&sem->wait_list)) {
+                /* hit end of list above */
+                adjustment -= RWSEM_WAITING_BIAS;
+        }
 
- out:
-        return sem;
+        if (adjustment)
+                atomic_long_add(adjustment, &sem->count);
 }
 
 /*
@@ -235,7 +227,6 @@ struct rw_semaphore __sched *rwsem_down_read_failed(struct rw_semaphore *sem)
         struct task_struct *tsk = current;
         WAKE_Q(wake_q);
 
-        /* set up my own style of waitqueue */
         waiter.task = tsk;
         waiter.type = RWSEM_WAITING_FOR_READ;
 
@@ -247,7 +238,8 @@ struct rw_semaphore __sched *rwsem_down_read_failed(struct rw_semaphore *sem)
         /* we're now waiting on the lock, but no longer actively locking */
         count = atomic_long_add_return(adjustment, &sem->count);
 
-        /* If there are no active locks, wake the front queued process(es).
+        /*
+         * If there are no active locks, wake the front queued process(es).
          *
          * If there are no writers and we are first in the queue,
          * wake our own waiter to join the existing active readers !
@@ -255,7 +247,7 @@ struct rw_semaphore __sched *rwsem_down_read_failed(struct rw_semaphore *sem)
         if (count == RWSEM_WAITING_BIAS ||
             (count > RWSEM_WAITING_BIAS &&
              adjustment != -RWSEM_ACTIVE_READ_BIAS))
-                sem = __rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
+                __rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
 
         raw_spin_unlock_irq(&sem->wait_lock);
         wake_up_q(&wake_q);
@@ -505,7 +497,7 @@ __rwsem_down_write_failed_common(struct rw_semaphore *sem, int state)
                 if (count > RWSEM_WAITING_BIAS) {
                         WAKE_Q(wake_q);
 
-                        sem = __rwsem_mark_wake(sem, RWSEM_WAKE_READERS, &wake_q);
+                        __rwsem_mark_wake(sem, RWSEM_WAKE_READERS, &wake_q);
                         /*
                          * The wakeup is normally called _after_ the wait_lock
                          * is released, but given that we are proactively waking
@@ -614,9 +606,8 @@ struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem)
         raw_spin_lock_irqsave(&sem->wait_lock, flags);
 locked:
 
-        /* do nothing if list empty */
         if (!list_empty(&sem->wait_list))
-                sem = __rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
+                __rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
 
         raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
         wake_up_q(&wake_q);
@@ -638,9 +629,8 @@ struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem)
 
         raw_spin_lock_irqsave(&sem->wait_lock, flags);
 
-        /* do nothing if list empty */
         if (!list_empty(&sem->wait_list))
-                sem = __rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED, &wake_q);
+                __rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED, &wake_q);
 
         raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
         wake_up_q(&wake_q);