On Wed, Jun 22, 2022 at 03:45:59PM -0400, Gabriel Krisman Bertazi wrote:
> +static inline int generic_ci_d_revalidate(struct dentry *dentry,
> + const struct qstr *name,
> + unsigned int flags)
> +{
> + int is_creation = flags & (LOOKUP_CREATE | LOOKUP_RENAME_TARGET);
> +
> + if (d_is_negative(dentry)) {
> + const struct dentry *parent = READ_ONCE(dentry->d_parent);
> + const struct inode *dir = READ_ONCE(parent->d_inode);
> +
> + if (dir && needs_casefold(dir)) {
> + if (!d_is_casefold_lookup(dentry))
> + return 0;
In which conditions does that happen?
> + if (is_creation &&
> + (dentry->d_name.len != name->len ||
> + memcmp(dentry->d_name.name, name->name, name->len)))
> + return 0;
> + }
> + }
> + return 1;
> +}
Analysis of stability of ->d_name, please. It's *probably* safe, but
the details are subtle and IMO should be accompanied by several asserts.
E.g. "we never get LOOKUP_CREATE in op->intent without O_CREAT in op->open_flag
for such and such reasons, and we verify that in such and such place"...
A part of that would be "the call in lookup_dcache() can only get there
with non-zero flags when coming from __lookup_hash(), and that has parent locked,
stabilizing the name; the same goes for the call in __lookup_slow(), with the
only call chain with possibly non-zero flags is through lookup_slow(), where we
have the parent locked". However, lookup_fast() and lookup_open() have the
flags come from nd->flags, and LOOKUP_CREATE can be found there in several areas.
I _think_ we are guaranteed the parent locked in all such call chains, but that
is definitely worth at least a comment.
