linux-ext4 - [RFC PATCH] ext4: use the normal helper to get the actual inode

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Date:   Sat, 10 Oct 2020 16:10:16 +0800
From:   xiakaixu1987@...il.com
To:     linux-ext4@...r.kernel.org
Cc:     tytso@....edu, adilger.kernel@...ger.ca,
        Kaixu Xia <kaixuxia@...cent.com>
Subject: [RFC PATCH] ext4: use the normal helper to get the actual inode

From: Kaixu Xia <kaixuxia@...cent.com>

Here we use the READ_ONCE to fix race conditions in ->d_compare() and
->d_hash() when they are called in RCU-walk mode, seems we can use
the normal helper d_inode_rcu() to get the actual inode.

Signed-off-by: Kaixu Xia <kaixuxia@...cent.com>
---
 fs/ext4/dir.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c
index 1d82336b1cd4..3bf6cb8e55f6 100644
--- a/fs/ext4/dir.c
+++ b/fs/ext4/dir.c
@@ -674,7 +674,7 @@ static int ext4_d_compare(const struct dentry *dentry, unsigned int len,
 {
 	struct qstr qstr = {.name = str, .len = len };
 	const struct dentry *parent = READ_ONCE(dentry->d_parent);
-	const struct inode *inode = READ_ONCE(parent->d_inode);
+	const struct inode *inode = d_inode_rcu(parent);
 	char strbuf[DNAME_INLINE_LEN];
 
 	if (!inode || !IS_CASEFOLDED(inode) ||
@@ -706,7 +706,7 @@ static int ext4_d_hash(const struct dentry *dentry, struct qstr *str)
 {
 	const struct ext4_sb_info *sbi = EXT4_SB(dentry->d_sb);
 	const struct unicode_map *um = sbi->s_encoding;
-	const struct inode *inode = READ_ONCE(dentry->d_inode);
+	const struct inode *inode = d_inode_rcu(dentry);
 	unsigned char *norm;
 	int len, ret = 0;
 
-- 
2.20.0