fscrypt: improve fscrypt_destroy_keyring() documentation

Document that fscrypt_destroy_keyring() must be called after all
potentially-encrypted inodes have been evicted.

Link: https://lore.kernel.org/r/20230313221231.272498-3-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>

diff --git a/fs/crypto/keyring.c b/fs/crypto/keyring.c
index 78086f8dbda5261f6b36a9fe8523debe81c97faa..bb15709ac9a40ad5eba5ee8bfdbf554d29096980 100644 (file)
--- a/fs/crypto/keyring.c
+++ b/fs/crypto/keyring.c
@@ -207,10 +207,11 @@ static int allocate_filesystem_keyring(struct super_block *sb)
  * Release all encryption keys that have been added to the filesystem, along
  * with the keyring that contains them.
  *
- * This is called at unmount time.  The filesystem's underlying block device(s)
- * are still available at this time; this is important because after user file
- * accesses have been allowed, this function may need to evict keys from the
- * keyslots of an inline crypto engine, which requires the block device(s).
+ * This is called at unmount time, after all potentially-encrypted inodes have
+ * been evicted.  The filesystem's underlying block device(s) are still
+ * available at this time; this is important because after user file accesses
+ * have been allowed, this function may need to evict keys from the keyslots of
+ * an inline crypto engine, which requires the block device(s).
  */
 void fscrypt_destroy_keyring(struct super_block *sb)
 {
@@ -227,12 +228,12 @@ void fscrypt_destroy_keyring(struct super_block *sb)
 
                hlist_for_each_entry_safe(mk, tmp, bucket, mk_node) {
                        /*
-                        * Since all inodes were already evicted, every key
-                        * remaining in the keyring should have an empty inode
-                        * list, and should only still be in the keyring due to
-                        * the single active ref associated with ->mk_secret.
-                        * There should be no structural refs beyond the one
-                        * associated with the active ref.
+                        * Since all potentially-encrypted inodes were already
+                        * evicted, every key remaining in the keyring should
+                        * have an empty inode list, and should only still be in
+                        * the keyring due to the single active ref associated
+                        * with ->mk_secret.  There should be no structural refs
+                        * beyond the one associated with the active ref.
                         */
                        WARN_ON(refcount_read(&mk->mk_active_refs) != 1);
                        WARN_ON(refcount_read(&mk->mk_struct_refs) != 1);