[RFC][PATCH 3/8] epoll: remove file from tfile_check_list when releasing file

[Hou Tao <houtao1@huawei.com>]

Before the removal of epmutex, the acquisition of epmutex in
eventpoll_release_file() will prevent the freeing of file, so
it's OK to iterate files in tfile_check_list.

And now epmutex is removed, so when releasing file, we need
to remove file from tfile_check_list to ensure the validity
of file.

Signed-off-by: Hou Tao <houtao1@huawei.com>
---
 fs/eventpoll.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 44ea587..998c635 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1029,6 +1029,18 @@ void eventpoll_release_file(struct file *file)
 		ep_remove(ep, epi);
 		mutex_unlock(&ep->mtx);
 	}
+
+	/*
+	 * The file can not been added to tfile_check_list again, because
+	 * (1) its refcnt has been zero, so ep_ctrl() can no longer get its reference
+	 * (2) its related ep items have been removed, so ep_loop_check_proc()
+	 *     can not get the file by ep->rbr
+	 */
+	if (!list_empty_careful(&file->f_tfile_llink)) {
+		mutex_lock(&epmutex);
+		list_del_init(&file->f_tfile_llink);
+		mutex_unlock(&epmutex);
+	}
 }
 
 static int ep_alloc(struct eventpoll **pep)
-- 
2.7.5