1 files changed, 50 insertions, 14 deletions

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 4a09af9e9a63..ed38801b57a7 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -62,7 +62,7 @@
  * This mutex is acquired by ep_free() during the epoll file
  * cleanup path and it is also acquired by eventpoll_release_file()
  * if a file has been pushed inside an epoll set and it is then
- * close()d without a previous call toepoll_ctl(EPOLL_CTL_DEL).
+ * close()d without a previous call to epoll_ctl(EPOLL_CTL_DEL).
  * It is also acquired when inserting an epoll fd onto another epoll
  * fd. We do this so that we walk the epoll tree and ensure that this
  * insertion does not create a cycle of epoll file descriptors, which
@@ -152,11 +152,11 @@ struct epitem {
 
 /*
  * This structure is stored inside the "private_data" member of the file
- * structure and rapresent the main data sructure for the eventpoll
+ * structure and represents the main data structure for the eventpoll
  * interface.
  */
 struct eventpoll {
-        /* Protect the this structure access */
+        /* Protect the access to this structure */
         spinlock_t lock;
 
         /*
@@ -316,6 +316,19 @@ static void ep_nested_calls_init(struct nested_calls *ncalls)
 }
 
 /**
+ * ep_events_available - Checks if ready events might be available.
+ *
+ * @ep: Pointer to the eventpoll context.
+ *
+ * Returns: Returns a value different than zero if ready events are available,
+ *          or zero otherwise.
+ */
+static inline int ep_events_available(struct eventpoll *ep)
+{
+        return !list_empty(&ep->rdllist) || ep->ovflist != EP_UNACTIVE_PTR;
+}
+
+/**
  * ep_call_nested - Perform a bound (possibly) nested call, by checking
  *                  that the recursion limit is not exceeded, and that
  *                  the same nested call (by the meaning of same cookie) is
@@ -793,7 +806,7 @@ static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd)
 
 /*
  * This is the callback that is passed to the wait queue wakeup
- * machanism. It is called by the stored file descriptors when they
+ * mechanism. It is called by the stored file descriptors when they
  * have events to report.
  */
 static int ep_poll_callback(wait_queue_t *wait, unsigned mode, int sync, void *key)
@@ -824,9 +837,9 @@ static int ep_poll_callback(wait_queue_t *wait, unsigned mode, int sync, void *k
                 goto out_unlock;
 
         /*
-         * If we are trasfering events to userspace, we can hold no locks
+         * If we are transferring events to userspace, we can hold no locks
          * (because we're accessing user memory, and because of linux f_op->poll()
-         * semantics). All the events that happens during that period of time are
+         * semantics). All the events that happen during that period of time are
          * chained in ep->ovflist and requeued later on.
          */
         if (unlikely(ep->ovflist != EP_UNACTIVE_PTR)) {
@@ -1135,12 +1148,29 @@ static inline struct timespec ep_set_mstimeout(long ms)
         return timespec_add_safe(now, ts);
 }
 
+/**
+ * ep_poll - Retrieves ready events, and delivers them to the caller supplied
+ *           event buffer.
+ *
+ * @ep: Pointer to the eventpoll context.
+ * @events: Pointer to the userspace buffer where the ready events should be
+ *          stored.
+ * @maxevents: Size (in terms of number of events) of the caller event buffer.
+ * @timeout: Maximum timeout for the ready events fetch operation, in
+ *           milliseconds. If the @timeout is zero, the function will not block,
+ *           while if the @timeout is less than zero, the function will block
+ *           until at least one event has been retrieved (or an error
+ *           occurred).
+ *
+ * Returns: Returns the number of ready events which have been fetched, or an
+ *          error code, in case of error.
+ */
 static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
                    int maxevents, long timeout)
 {
-        int res, eavail, timed_out = 0;
+        int res = 0, eavail, timed_out = 0;
         unsigned long flags;
-        long slack;
+        long slack = 0;
         wait_queue_t wait;
         ktime_t expires, *to = NULL;
 
@@ -1151,14 +1181,19 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
                 to = &expires;
                 *to = timespec_to_ktime(end_time);
         } else if (timeout == 0) {
+                /*
+                 * Avoid the unnecessary trip to the wait queue loop, if the
+                 * caller specified a non blocking operation.
+                 */
                 timed_out = 1;
+                spin_lock_irqsave(&ep->lock, flags);
+                goto check_events;
         }
 
-retry:
+fetch_events:
         spin_lock_irqsave(&ep->lock, flags);
 
-        res = 0;
-        if (list_empty(&ep->rdllist)) {
+        if (!ep_events_available(ep)) {
                 /*
                  * We don't have any available event to return to the caller.
                  * We need to sleep here, and we will be wake up by
@@ -1174,7 +1209,7 @@ retry:
                          * to TASK_INTERRUPTIBLE before doing the checks.
                          */
                         set_current_state(TASK_INTERRUPTIBLE);
-                        if (!list_empty(&ep->rdllist) || timed_out)
+                        if (ep_events_available(ep) || timed_out)
                                 break;
                         if (signal_pending(current)) {
                                 res = -EINTR;
@@ -1191,8 +1226,9 @@ retry:
 
                 set_current_state(TASK_RUNNING);
         }
+check_events:
         /* Is it worth to try to dig for events ? */
-        eavail = !list_empty(&ep->rdllist) || ep->ovflist != EP_UNACTIVE_PTR;
+        eavail = ep_events_available(ep);
 
         spin_unlock_irqrestore(&ep->lock, flags);
 
@@ -1203,7 +1239,7 @@ retry:
          */
         if (!res && eavail &&
             !(res = ep_send_events(ep, events, maxevents)) && !timed_out)
-                goto retry;
+                goto fetch_events;
 
         return res;
 }