1 files changed, 88 insertions, 0 deletions

diff --git a/kernel/wait.c b/kernel/wait.c
index 6698e0c04ead..d550920e040c 100644
--- a/kernel/wait.c
+++ b/kernel/wait.c
@@ -287,3 +287,91 @@ wait_queue_head_t *bit_waitqueue(void *word, int bit)
         return &zone->wait_table[hash_long(val, zone->wait_table_bits)];
 }
 EXPORT_SYMBOL(bit_waitqueue);
+
+/*
+ * Manipulate the atomic_t address to produce a better bit waitqueue table hash
+ * index (we're keying off bit -1, but that would produce a horrible hash
+ * value).
+ */
+static inline wait_queue_head_t *atomic_t_waitqueue(atomic_t *p)
+{
+        if (BITS_PER_LONG == 64) {
+                unsigned long q = (unsigned long)p;
+                return bit_waitqueue((void *)(q & ~1), q & 1);
+        }
+        return bit_waitqueue(p, 0);
+}
+
+static int wake_atomic_t_function(wait_queue_t *wait, unsigned mode, int sync,
+                                  void *arg)
+{
+        struct wait_bit_key *key = arg;
+        struct wait_bit_queue *wait_bit
+                = container_of(wait, struct wait_bit_queue, wait);
+        atomic_t *val = key->flags;
+
+        if (wait_bit->key.flags != key->flags ||
+            wait_bit->key.bit_nr != key->bit_nr ||
+            atomic_read(val) != 0)
+                return 0;
+        return autoremove_wake_function(wait, mode, sync, key);
+}
+
+/*
+ * To allow interruptible waiting and asynchronous (i.e. nonblocking) waiting,
+ * the actions of __wait_on_atomic_t() are permitted return codes.  Nonzero
+ * return codes halt waiting and return.
+ */
+static __sched
+int __wait_on_atomic_t(wait_queue_head_t *wq, struct wait_bit_queue *q,
+                       int (*action)(atomic_t *), unsigned mode)
+{
+        atomic_t *val;
+        int ret = 0;
+
+        do {
+                prepare_to_wait(wq, &q->wait, mode);
+                val = q->key.flags;
+                if (atomic_read(val) == 0)
+                        break;
+                ret = (*action)(val);
+        } while (!ret && atomic_read(val) != 0);
+        finish_wait(wq, &q->wait);
+        return ret;
+}
+
+#define DEFINE_WAIT_ATOMIC_T(name, p)                                   \
+        struct wait_bit_queue name = {                                  \
+                .key = __WAIT_ATOMIC_T_KEY_INITIALIZER(p),              \
+                .wait   = {                                             \
+                        .private        = current,                      \
+                        .func           = wake_atomic_t_function,       \
+                        .task_list      =                               \
+                                LIST_HEAD_INIT((name).wait.task_list),  \
+                },                                                      \
+        }
+
+__sched int out_of_line_wait_on_atomic_t(atomic_t *p, int (*action)(atomic_t *),
+                                         unsigned mode)
+{
+        wait_queue_head_t *wq = atomic_t_waitqueue(p);
+        DEFINE_WAIT_ATOMIC_T(wait, p);
+
+        return __wait_on_atomic_t(wq, &wait, action, mode);
+}
+EXPORT_SYMBOL(out_of_line_wait_on_atomic_t);
+
+/**
+ * wake_up_atomic_t - Wake up a waiter on a atomic_t
+ * @p: The atomic_t being waited on, a kernel virtual address
+ *
+ * Wake up anyone waiting for the atomic_t to go to zero.
+ *
+ * Abuse the bit-waker function and its waitqueue hash table set (the atomic_t
+ * check is done by the waiter's wake function, not the by the waker itself).
+ */
+void wake_up_atomic_t(atomic_t *p)
+{
+        __wake_up_bit(atomic_t_waitqueue(p), p, WAIT_ATOMIC_T_BIT_NR);
+}
+EXPORT_SYMBOL(wake_up_atomic_t);