[PATCH 2/9] eventpoll: add helper to remove wait entry from wait queue head

[Jens Axboe <axboe@kernel.dk>]

__epoll_wait_remove() is the core helper, it kills a given
wait_queue_entry from the eventpoll wait_queue_head. Use it internally,
and provide an overall helper, epoll_wait_remove(), which takes a struct
file and provides the same functionality.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/eventpoll.c            | 58 +++++++++++++++++++++++++--------------
 include/linux/eventpoll.h |  3 ++
 2 files changed, 40 insertions(+), 21 deletions(-)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 73b639caed3d..01edbee5c766 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1980,6 +1980,42 @@ static int ep_autoremove_wake_function(struct wait_queue_entry *wq_entry,
 	return ret;
 }
 
+static int __epoll_wait_remove(struct eventpoll *ep,
+			       struct wait_queue_entry *wait, int timed_out)
+{
+	int eavail;
+
+	/*
+	 * We were woken up, thus go and try to harvest some events. If timed
+	 * out and still on the wait queue, recheck eavail carefully under
+	 * lock, below.
+	 */
+	eavail = 1;
+
+	if (!list_empty_careful(&wait->entry)) {
+		write_lock_irq(&ep->lock);
+		/*
+		 * If the thread timed out and is not on the wait queue, it
+		 * means that the thread was woken up after its timeout expired
+		 * before it could reacquire the lock. Thus, when wait.entry is
+		 * empty, it needs to harvest events.
+		 */
+		if (timed_out)
+			eavail = list_empty(&wait->entry);
+		__remove_wait_queue(&ep->wq, wait);
+		write_unlock_irq(&ep->lock);
+	}
+
+	return eavail;
+}
+
+int epoll_wait_remove(struct file *file, struct wait_queue_entry *wait)
+{
+	if (is_file_epoll(file))
+		return __epoll_wait_remove(file->private_data, wait, false);
+	return -EINVAL;
+}
+
 /**
  * ep_poll - Retrieves ready events, and delivers them to the caller-supplied
  *           event buffer.
@@ -2100,27 +2136,7 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
 							      HRTIMER_MODE_ABS);
 		__set_current_state(TASK_RUNNING);
 
-		/*
-		 * We were woken up, thus go and try to harvest some events.
-		 * If timed out and still on the wait queue, recheck eavail
-		 * carefully under lock, below.
-		 */
-		eavail = 1;
-
-		if (!list_empty_careful(&wait.entry)) {
-			write_lock_irq(&ep->lock);
-			/*
-			 * If the thread timed out and is not on the wait queue,
-			 * it means that the thread was woken up after its
-			 * timeout expired before it could reacquire the lock.
-			 * Thus, when wait.entry is empty, it needs to harvest
-			 * events.
-			 */
-			if (timed_out)
-				eavail = list_empty(&wait.entry);
-			__remove_wait_queue(&ep->wq, &wait);
-			write_unlock_irq(&ep->lock);
-		}
+		eavail = __epoll_wait_remove(ep, &wait, timed_out);
 	}
 }
 
diff --git a/include/linux/eventpoll.h b/include/linux/eventpoll.h
index f37fea931c44..1301fc74aca0 100644
--- a/include/linux/eventpoll.h
+++ b/include/linux/eventpoll.h
@@ -29,6 +29,9 @@ void eventpoll_release_file(struct file *file);
 int epoll_wait(struct file *file, struct epoll_event __user *events,
 	       int maxevents, struct timespec64 *to);
 
+/* Remove wait entry */
+int epoll_wait_remove(struct file *file, struct wait_queue_entry *wait);
+
 /*
  * This is called from inside fs/file_table.c:__fput() to unlink files
  * from the eventpoll interface. We need to have this facility to cleanup
-- 
2.47.2