CPU0				CPU1

	journal_get_write_access(bh)
	 (Add buffer to t_reserved_list)

					journal_get_write_access(bh)
					 (It's already on t_reserved_list:
					  nothing to do)

	 (We decide we don't want to
	  journal the buffer after all)
	journal_release_buffer()
	 (It gets pulled off the transaction)


					journal_dirty_metadata()
					 (The buffer isn't on the reserved
					  list!  The kernel explodes)


Simple fix: just leave the buffer on t_reserved_list in
journal_release_buffer().  If nobody ends up claiming the buffer then it will
get thrown away at start of transaction commit.