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-rw-r--r--fs/eventpoll.c33
1 files changed, 28 insertions, 5 deletions
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 57298d092f56..ed38801b57a7 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1148,12 +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;
@@ -1164,13 +1181,18 @@ 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 (!ep_events_available(ep)) {
/*
* We don't have any available event to return to the caller.
@@ -1204,6 +1226,7 @@ retry:
set_current_state(TASK_RUNNING);
}
+check_events:
/* Is it worth to try to dig for events ? */
eavail = ep_events_available(ep);
@@ -1216,7 +1239,7 @@ retry:
*/
if (!res && eavail &&
!(res = ep_send_events(ep, events, maxevents)) && !timed_out)
- goto retry;
+ goto fetch_events;
return res;
}