[PATCH] fs: f2fs: fix kernel discard_thread NULL dereference

[Hoi Pok Wu]

Pointer discard_thread is pointing to nowhere, using IS_ERR prevents the
situation. IS_ERR also seen being used throughout the file.

Link: https://syzkaller.appspot.com/bug?id=9499bc6574cea5940e48199c2fd0732d9b11e5e1
Reported-by: syzbot+035a381ea1afb63f098d@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Hoi Pok Wu <wuhoipok@xxxxxxxxx>
---
 fs/f2fs/segment.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index acf3d3fa4363..79978b7206b5 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -1634,7 +1634,8 @@ void f2fs_stop_discard_thread(struct f2fs_sb_info *sbi)
 		struct task_struct *discard_thread = dcc->f2fs_issue_discard;
 
 		dcc->f2fs_issue_discard = NULL;
-		kthread_stop(discard_thread);
+		if (!IS_ERR(discard_thread))
+			kthread_stop(discard_thread);
 	}
 }
 
-- 
2.38.0