ext4: destroy ext4_fc_dentry_cachep kmemcache on module removal

The kmemcache for ext4_fc_dentry_cachep remains registered after module
removal.

Destroy ext4_fc_dentry_cachep kmemcache on module removal.

Fixes: aa75f4d ("ext4: main fast-commit commit path")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Lukas Czerner <lczerner@redhat.com>
Reviewed-by: Harshad Shirwadkar <harshadshirwadkar@gmail.com>
Link: https://lore.kernel.org/r/20211110134640.lyku5vklvdndw6uk@linutronix.de
Link: https://lore.kernel.org/r/YbiK3JetFFl08bd7@linutronix.de
Link: https://lore.kernel.org/r/20211223164436.2628390-1-bigeasy@linutronix.de
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org

fs/ext4/ext4.h

@@ -2932,6 +2932,7 @@ bool ext4_fc_replay_check_excluded(struct super_block *sb, ext4_fsblk_t block);
 void ext4_fc_replay_cleanup(struct super_block *sb);
 int ext4_fc_commit(journal_t *journal, tid_t commit_tid);
 int __init ext4_fc_init_dentry_cache(void);
+void ext4_fc_destroy_dentry_cache(void);
 
 /* mballoc.c */
 extern const struct seq_operations ext4_mb_seq_groups_ops;

fs/ext4/fast_commit.c

@@ -2153,3 +2153,8 @@ int __init ext4_fc_init_dentry_cache(void)
 
 	return 0;
 }
+
+void ext4_fc_destroy_dentry_cache(void)
+{
+	kmem_cache_destroy(ext4_fc_dentry_cachep);
+}

fs/ext4/super.c

@@ -7118,6 +7118,7 @@ static int __init ext4_init_fs(void)
 out:
 	unregister_as_ext2();
 	unregister_as_ext3();
+	ext4_fc_destroy_dentry_cache();
 out05:
 	destroy_inodecache();
 out1:
@@ -7144,6 +7145,7 @@ static void __exit ext4_exit_fs(void)
 	unregister_as_ext2();
 	unregister_as_ext3();
 	unregister_filesystem(&ext4_fs_type);
+	ext4_fc_destroy_dentry_cache();
 	destroy_inodecache();
 	ext4_exit_mballoc();
 	ext4_exit_sysfs();