ext4: use the normal helper to get the actual inode

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@tencent.com>
Reviewed-by: Lukas Czerner <lczerner@redhat.com>
Link: https://lore.kernel.org/r/1602317416-1260-1-git-send-email-kaixuxia@tencent.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c
index 1d82336..3bf6cb8 100644 (file)
--- 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;