On Mon, Jun 09, 2025 at 05:34:12PM +1000, NeilBrown wrote:
> After taking the directory lock (or locks) we now lock the target
> dentries. This is pointless at present but will allow us to remove the
> taking of the directory lock in a future patch.
>
> MORE WORDS
Such as "why doesn't it deadlock?", presumably, seeing that you have
> @@ -2003,7 +2003,14 @@ struct dentry *lookup_and_lock_hashed(struct qstr *last,
>
> inode_lock_nested(base->d_inode, I_MUTEX_PARENT);
>
> +retry:
> dentry = lookup_one_qstr(last, base, lookup_flags);
> + if (!IS_ERR(dentry) &&
> + !dentry_lock(dentry, base, last, TASK_UNINTERRUPTIBLE)) {
... take dentry lock inside ->i_rwsem on parent and
> bool lock_and_check_dentry(struct dentry *child, struct dentry *parent)
> {
> - inode_lock_nested(d_inode(parent), I_MUTEX_PARENT);
> - if (child->d_parent == parent) {
> - /* get the child to balance with dentry_unlock which puts it. */
> - dget(child);
> - return true;
> + if (!dentry_lock(child, NULL, NULL, TASK_UNINTERRUPTIBLE))
> + return false;
> + if (child->d_parent != parent) {
> + __dentry_unlock(child);
> + return false;
> }
> - inode_unlock(d_inode(parent));
> - return false;
> + /* get the child to balance with dentry_unlock() which puts it. */
> + dget(child);
> + inode_lock_nested(d_inode(parent), I_MUTEX_PARENT);
... do the same in opposite order?
How could that possibly work?
