ext4: unregister sysfs path before destroying jbd2 journal

mainline inclusion
from mainline-v5.7-rc1
commit 5e47868f
category: bugfix
bugzilla: 186675, https://gitee.com/openeuler/kernel/issues/I55TUC


CVE: NA

-------------------------------------------------

Call ext4_unregister_sysfs(), before destroying jbd2 journal,
since below might cause, NULL pointer dereference issue.
This got reported with LTP tests.

ext4_put_super() 		cat /sys/fs/ext4/loop2/journal_task
	| 				ext4_attr_show();
ext4_jbd2_journal_destroy();  			|
    	|				 journal_task_show()
	| 					|
	| 				task_pid_vnr(NULL);
sbi->s_journal = NULL;

Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20200318061301.4320-1-riteshh@linux.ibm.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>

conflicts:
	fs/ext4/super.c

Signed-off-by: ChenXiaoSong <chenxiaosong2@huawei.com>
Reviewed-by: yebin <yebin10@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>