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Date:   Mon, 19 Jul 2021 13:59:14 +0800
From:   Xiyu Yang <xiyuyang19@...an.edu.cn>
To:     "Theodore Ts'o" <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     yuanxzhang@...an.edu.cn, Xiyu Yang <xiyuyang19@...an.edu.cn>,
        Xin Tan <tanxin.ctf@...il.com>
Subject: [PATCH] ext4: Convert from atomic_t to refcount_t on ext4_io_end->count

refcount_t type and corresponding API can protect refcounters from
accidental underflow and overflow and further use-after-free situations.

Signed-off-by: Xiyu Yang <xiyuyang19@...an.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@...il.com>
---
 fs/ext4/ext4.h    | 3 ++-
 fs/ext4/page-io.c | 8 ++++----
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 3c51e243450d..e5b3575da7e9 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -17,6 +17,7 @@
 #ifndef _EXT4_H
 #define _EXT4_H
 
+#include <linux/refcount.h>
 #include <linux/types.h>
 #include <linux/blkdev.h>
 #include <linux/magic.h>
@@ -241,7 +242,7 @@ typedef struct ext4_io_end {
 	struct bio		*bio;		/* Linked list of completed
 						 * bios covering the extent */
 	unsigned int		flag;		/* unwritten or not */
-	atomic_t		count;		/* reference counter */
+	refcount_t		count;		/* reference counter */
 	struct list_head	list_vec;	/* list of ext4_io_end_vec */
 } ext4_io_end_t;
 
diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index f038d578d8d8..9cb261714991 100644
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -279,14 +279,14 @@ ext4_io_end_t *ext4_init_io_end(struct inode *inode, gfp_t flags)
 		io_end->inode = inode;
 		INIT_LIST_HEAD(&io_end->list);
 		INIT_LIST_HEAD(&io_end->list_vec);
-		atomic_set(&io_end->count, 1);
+		refcount_set(&io_end->count, 1);
 	}
 	return io_end;
 }
 
 void ext4_put_io_end_defer(ext4_io_end_t *io_end)
 {
-	if (atomic_dec_and_test(&io_end->count)) {
+	if (refcount_dec_and_test(&io_end->count)) {
 		if (!(io_end->flag & EXT4_IO_END_UNWRITTEN) ||
 				list_empty(&io_end->list_vec)) {
 			ext4_release_io_end(io_end);
@@ -300,7 +300,7 @@ int ext4_put_io_end(ext4_io_end_t *io_end)
 {
 	int err = 0;
 
-	if (atomic_dec_and_test(&io_end->count)) {
+	if (refcount_dec_and_test(&io_end->count)) {
 		if (io_end->flag & EXT4_IO_END_UNWRITTEN) {
 			err = ext4_convert_unwritten_io_end_vec(io_end->handle,
 								io_end);
@@ -314,7 +314,7 @@ int ext4_put_io_end(ext4_io_end_t *io_end)
 
 ext4_io_end_t *ext4_get_io_end(ext4_io_end_t *io_end)
 {
-	atomic_inc(&io_end->count);
+	refcount_inc(&io_end->count);
 	return io_end;
 }
 
-- 
2.7.4

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