ext4: fix a double free in ext4_register_li_request

ext4: fix a double free in ext4_register_li_request

BugLink: http://bugs.launchpad.net/bugs/761134

commit 46e4690bbd9a4f8d9e7c4f34e34b48f703ad47e0 upstream.

In ext4_register_li_request, we malloc a ext4_li_request and
inserts it into ext4_li_info->li_request_list. In case of any
error later, we free it in the end.  But if we have some error
in ext4_run_lazyinit_thread, the whole li_request_list will be
dropped and freed in it. So we will double free this ext4_li_request.

This patch just sets elr to NULL after it is inserted to the list
so that the latter kfree won't double free it.

Signed-off-by: Tao Ma <boyu.mt@taobao.com>
Reviewed-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>