jbd2: allocate transaction from separate slab cache

There is normally only a handful of these active at any one time, but
putting them in a separate slab cache makes debugging memory
corruption problems easier.  Manish Katiyar also wanted this make it
easier to test memory failure scenarios in the jbd2 layer.

Cc: Manish Katiyar <mkatiyar@gmail.com>
Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
index 453c906..253e9189 100644
--- a/fs/jbd2/checkpoint.c
+++ b/fs/jbd2/checkpoint.c
@@ -722,7 +722,7 @@
 				    transaction->t_tid, stats);
 
 	__jbd2_journal_drop_transaction(journal, transaction);
-	kfree(transaction);
+	jbd2_journal_free_transaction(transaction);
 
 	/* Just in case anybody was waiting for more transactions to be
            checkpointed... */