[PATCH 4/7] step_into(): lose inode argument

Al Viro
2022-07-04T23:16:00Z

make handle_mounts() always fetch it. This is just the first step -
the callers of step_into() will stop trying to calculate the sucker,
etc.

The passed value should be equal to dentry->d_inode in all cases;
in RCU mode - fetched after we'd sampled ->d_seq. Might as well
fetch it here. We do need to validate ->d_seq, which duplicates
the check currently done in lookup_fast(); that duplication will
go away shortly.

After that change handle_mounts() always ignores the initial value of
*inode and always sets it on success.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
fs/namei.c | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index c7c9e88add85..dddbebf92b48 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1532,6 +1532,11 @@ static inline int handle_mounts(struct nameidata *nd, struct dentry *dentry,
path->dentry = dentry;
if (nd->flags & LOOKUP_RCU) {
unsigned int seq = nd->next_seq;
+ *inode = dentry->d_inode;
+ if (read_seqcount_retry(&dentry->d_seq, seq))
+ return -ECHILD;
+ if (unlikely(!*inode))
+ return -ENOENT;
if (likely(__follow_mount_rcu(nd, path, inode)))
return 0;
// *path and nd->next_seq might've been clobbered
@@ -1842,9 +1847,10 @@ static const char *pick_link(struct nameidata *nd, struct path *link,
* NOTE: dentry must be what nd->next_seq had been sampled from.
*/
static const char *step_into(struct nameidata *nd, int flags,
- struct dentry *dentry, struct inode *inode)
+ struct dentry *dentry)
{
struct path path;
+ struct inode *inode;
int err = handle_mounts(nd, dentry, &path, &inode);

if (err < 0)
@@ -1970,7 +1976,7 @@ static const char *handle_dots(struct nameidata *nd, int type)
parent = follow_dotdot(nd, &inode);
if (IS_ERR(parent))
return ERR_CAST(parent);
- error = step_into(nd, WALK_NOFOLLOW, parent, inode);
+ error = step_into(nd, WALK_NOFOLLOW, parent);
if (unlikely(error))
return error;

@@ -2015,7 +2021,7 @@ static const char *walk_component(struct nameidata *nd, int flags)
}
if (!(flags & WALK_MORE) && nd->depth)
put_link(nd);
- return step_into(nd, flags, dentry, inode);
+ return step_into(nd, flags, dentry);
}

/*
@@ -2474,8 +2480,7 @@ static int handle_lookup_down(struct nameidata *nd)
if (!(nd->flags & LOOKUP_RCU))
dget(nd->path.dentry);
nd->next_seq = nd->seq;
- return PTR_ERR(step_into(nd, WALK_NOFOLLOW,
- nd->path.dentry, nd->inode));
+ return PTR_ERR(step_into(nd, WALK_NOFOLLOW, nd->path.dentry));
}

/* Returns 0 and nd will be valid on success; Retuns error, otherwise. */
@@ -3464,7 +3469,7 @@ static const char *open_last_lookups(struct nameidata *nd,
finish_lookup:
if (nd->depth)
put_link(nd);
- res = step_into(nd, WALK_TRAILING, dentry, inode);
+ res = step_into(nd, WALK_TRAILING, dentry);
if (unlikely(res))
nd->flags &= ~(LOOKUP_OPEN|LOOKUP_CREATE|LOOKUP_EXCL);
return res;
--
2.30.2