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Diffstat (limited to 'fs/eventpoll.c')
-rw-r--r--fs/eventpoll.c60
1 files changed, 48 insertions, 12 deletions
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index ff12f7ac73ef..f9cfd168fbe2 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -181,7 +181,7 @@ struct eventpoll {
/*
* This is a single linked list that chains all the "struct epitem" that
- * happened while transfering ready events to userspace w/out
+ * happened while transferring ready events to userspace w/out
* holding ->lock.
*/
struct epitem *ovflist;
@@ -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
@@ -593,7 +606,7 @@ static void ep_free(struct eventpoll *ep)
* We do not need to hold "ep->mtx" here because the epoll file
* is on the way to be removed and no one has references to it
* anymore. The only hit might come from eventpoll_release_file() but
- * holding "epmutex" is sufficent here.
+ * holding "epmutex" is sufficient here.
*/
mutex_lock(&epmutex);
@@ -707,7 +720,7 @@ void eventpoll_release_file(struct file *file)
/*
* We don't want to get "file->f_lock" because it is not
* necessary. It is not necessary because we're in the "struct file"
- * cleanup path, and this means that noone is using this file anymore.
+ * cleanup path, and this means that no one is using this file anymore.
* So, for example, epoll_ctl() cannot hit here since if we reach this
* point, the file counter already went to zero and fget() would fail.
* The only hit might come from ep_free() but by holding the mutex
@@ -1099,7 +1112,7 @@ static int ep_send_events_proc(struct eventpoll *ep, struct list_head *head,
* Trigger mode, we need to insert back inside
* the ready list, so that the next call to
* epoll_wait() will check again the events
- * availability. At this point, noone can insert
+ * availability. At this point, no one can insert
* into ep->rdllist besides us. The epoll_ctl()
* callers are locked out by
* ep_scan_ready_list() holding "mtx" and the
@@ -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;
}