Re: [PATCH v2 08/20] afs_d_revalidate(): use stable name and parent inode passed by caller

Al Viro
2025-01-22T21:24:58Z

On Wed, Jan 22, 2025 at 09:01:24PM +0000, Al Viro wrote:
> On Wed, Jan 22, 2025 at 08:27:41PM +0000, David Howells wrote:
> > Al Viro <viro@zeniv.linux.org.uk> wrote:
> >
> > > - _enter("{%lu},%p{%pd},", dir->i_ino, dentry, dentry);
> > > + _enter("{%lu},{%s},", dir->i_ino, name->name);
> >
> > I don't think that name->name is guaranteed to be NUL-terminated after
> > name->len characters. The following:
> >
> > _enter("{%lu},{%*s},", dir->i_ino, name->len, name->name);
> >
> > might be better, though:
> >
> > _enter("{%lu},{%*.*s},", dir->i_ino, name->len, name->len, name->name);
> >
> > might be necessary.
>
> Good catch (and that definitely needs to be documented in previous commit),
> but what's wrong with
> _enter("{%lu},{%.*s},", dir->i_ino, name->len, name->name);

IOW, are you OK with the following?

commit bf61e4013ab1cb9a819303faca018e7b7cbaf3e7
Author: Al Viro <viro@zeniv.linux.org.uk>
Date: Fri Jan 3 00:27:27 2025 -0500

afs_d_revalidate(): use stable name and parent inode passed by caller

No need to bother with boilerplate for obtaining the latter and for
the former we really should not count upon ->d_name.name remaining
stable under us.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/afs/dir.c b/fs/afs/dir.c
index 9780013cd83a..e04cffe4beb1 100644
--- a/fs/afs/dir.c
+++ b/fs/afs/dir.c
@@ -607,19 +607,19 @@ static bool afs_lookup_one_filldir(struct dir_context *ctx, const char *name,
* Do a lookup of a single name in a directory
* - just returns the FID the dentry name maps to if found
*/
-static int afs_do_lookup_one(struct inode *dir, struct dentry *dentry,
+static int afs_do_lookup_one(struct inode *dir, const struct qstr *name,
struct afs_fid *fid, struct key *key,
afs_dataversion_t *_dir_version)
{
struct afs_super_info *as = dir->i_sb->s_fs_info;
struct afs_lookup_one_cookie cookie = {
.ctx.actor = afs_lookup_one_filldir,
- .name = dentry->d_name,
+ .name = *name,
.fid.vid = as->volume->vid
};
int ret;

- _enter("{%lu},%p{%pd},", dir->i_ino, dentry, dentry);
+ _enter("{%lu},{%.*s},", dir->i_ino, name->len, name->name);

/* search the directory */
ret = afs_dir_iterate(dir, &cookie.ctx, key, _dir_version);
@@ -1052,21 +1052,12 @@ static struct dentry *afs_lookup(struct inode *dir, struct dentry *dentry,
/*
* Check the validity of a dentry under RCU conditions.
*/
-static int afs_d_revalidate_rcu(struct dentry *dentry)
+static int afs_d_revalidate_rcu(struct afs_vnode *dvnode, struct dentry *dentry)
{
- struct afs_vnode *dvnode;
- struct dentry *parent;
- struct inode *dir;
long dir_version, de_version;

_enter("%p", dentry);

- /* Check the parent directory is still valid first. */
- parent = READ_ONCE(dentry->d_parent);
- dir = d_inode_rcu(parent);
- if (!dir)
- return -ECHILD;
- dvnode = AFS_FS_I(dir);
if (test_bit(AFS_VNODE_DELETED, &dvnode->flags))
return -ECHILD;

@@ -1097,9 +1088,8 @@ static int afs_d_revalidate_rcu(struct dentry *dentry)
static int afs_d_revalidate(struct inode *parent_dir, const struct qstr *name,
struct dentry *dentry, unsigned int flags)
{
- struct afs_vnode *vnode, *dir;
+ struct afs_vnode *vnode, *dir = AFS_FS_I(parent_dir);
struct afs_fid fid;
- struct dentry *parent;
struct inode *inode;
struct key *key;
afs_dataversion_t dir_version, invalid_before;
@@ -1107,7 +1097,7 @@ static int afs_d_revalidate(struct inode *parent_dir, const struct qstr *name,
int ret;

if (flags & LOOKUP_RCU)
- return afs_d_revalidate_rcu(dentry);
+ return afs_d_revalidate_rcu(dir, dentry);

if (d_really_is_positive(dentry)) {
vnode = AFS_FS_I(d_inode(dentry));
@@ -1122,14 +1112,9 @@ static int afs_d_revalidate(struct inode *parent_dir, const struct qstr *name,
if (IS_ERR(key))
key = NULL;

- /* Hold the parent dentry so we can peer at it */
- parent = dget_parent(dentry);
- dir = AFS_FS_I(d_inode(parent));
-
/* validate the parent directory */
ret = afs_validate(dir, key);
if (ret == -ERESTARTSYS) {
- dput(parent);
key_put(key);
return ret;
}
@@ -1157,7 +1142,7 @@ static int afs_d_revalidate(struct inode *parent_dir, const struct qstr *name,
afs_stat_v(dir, n_reval);

/* search the directory for this vnode */
- ret = afs_do_lookup_one(&dir->netfs.inode, dentry, &fid, key, &dir_version);
+ ret = afs_do_lookup_one(&dir->netfs.inode, name, &fid, key, &dir_version);
switch (ret) {
case 0:
/* the filename maps to something */
@@ -1201,22 +1186,19 @@ static int afs_d_revalidate(struct inode *parent_dir, const struct qstr *name,
goto out_valid;

default:
- _debug("failed to iterate dir %pd: %d",
- parent, ret);
+ _debug("failed to iterate parent %pd2: %d", dentry, ret);
goto not_found;
}

out_valid:
dentry->d_fsdata = (void *)(unsigned long)dir_version;
out_valid_noupdate:
- dput(parent);
key_put(key);
_leave(" = 1 [valid]");
return 1;

not_found:
_debug("dropping dentry %pd2", dentry);
- dput(parent);
key_put(key);

_leave(" = 0 [bad]");