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-rw-r--r--fs/eventpoll.c64
1 files changed, 50 insertions, 14 deletions
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 4a09af9e9a6..ed38801b57a 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;
}