vfs: document d_dispose_if_unused()

Add a warning about the danger of using this function without proper
locking preventing eviction.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Link: https://patch.msgid.link/20260114145344.468856-7-mszeredi@redhat.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: Miklos Szeredi

fs/dcache.c

@@ -1104,6 +1104,16 @@ struct dentry *d_find_alias_rcu(struct inode *inode)
 	return de;
 }
 
+/**
+ * d_dispose_if_unused - move unreferenced dentries to shrink list
+ * @dentry: dentry in question
+ * @dispose: head of shrink list
+ *
+ * If dentry has no external references, move it to shrink list.
+ *
+ * NOTE!!! The caller is responsible for preventing eviction of the dentry by
+ * holding dentry->d_inode->i_lock or equivalent.
+ */
 void d_dispose_if_unused(struct dentry *dentry, struct list_head *dispose)
 {
 	spin_lock(&dentry->d_lock);