2020-10-10 09:31:13

by Kaixu Xia

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

From: Kaixu Xia <[email protected]>

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 <[email protected]>
---
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

2020-10-12 09:36:17

by Lukas Czerner

Subject: Re: [RFC PATCH] ext4: use the normal helper to get the actual inode

On Sat, Oct 10, 2020 at 04:10:16PM +0800, [email protected] wrote:
> From: Kaixu Xia <[email protected]>
>
> 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.

Looks good to me.
Thanks!

Reviewed-by: Lukas Czerner <[email protected]>

>
> Signed-off-by: Kaixu Xia <[email protected]>
> ---
> 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
>

2020-10-14 17:39:31

by Theodore Ts'o

Subject: Re: [RFC PATCH] ext4: use the normal helper to get the actual inode

On Mon, Oct 12, 2020 at 11:33:04AM +0200, Lukas Czerner wrote:
> On Sat, Oct 10, 2020 at 04:10:16PM +0800, [email protected] wrote:
> > From: Kaixu Xia <[email protected]>
> >
> > 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.
>
> Looks good to me.
> Thanks!
>
> Reviewed-by: Lukas Czerner <[email protected]>

Thanks, applied.

- Ted