linux-kernel - [RFC][PATCH 3/8] epoll: remove file from tfile_check

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Date:   Sat, 28 Oct 2017 20:58:22 +0800
From:   Hou Tao <houtao1@...wei.com>
To:     <linux-fsdevel@...r.kernel.org>
CC:     <linux-kernel@...r.kernel.org>, <viro@...iv.linux.org.uk>,
        <jbaron@...mai.com>, <oleg@...hat.com>, <dave@...olabs.net>,
        <koct9i@...il.com>
Subject: [RFC][PATCH 3/8] epoll: remove file from tfile_check_list when releasing file

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@...wei.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