UBIFS: Add an assertion for clean_zn_cnt

This patch adds a new ubifs_assert() in ubifs_tnc_close() to check
if there are any leaks of per-filesystem @clean_zn_cnt. This new
assert inspects whether the return value of ubifs_destroy_tnc_subtree()
is equal to @clean_zn_cnt or not while umount.

Artem: a minor amendment
Signed-off-by: Nhujianyang <hujianyang@huawei.com>
Signed-off-by: NArtem Bityutskiy <artem.bityutskiy@linux.intel.com>

fs/ubifs/tnc.c

@@ -2859,10 +2859,11 @@ void ubifs_tnc_close(struct ubifs_info *c)
 {
 	tnc_destroy_cnext(c);
 	if (c->zroot.znode) {
-		long n;
+		long n, freed;
 
-		ubifs_destroy_tnc_subtree(c->zroot.znode);
 		n = atomic_long_read(&c->clean_zn_cnt);
+		freed = ubifs_destroy_tnc_subtree(c->zroot.znode);
+		ubifs_assert(freed == n);
 		atomic_long_sub(n, &ubifs_clean_zn_cnt);
 	}
 	kfree(c->gap_lebs);