EX-2723 kernel: fix potential infinite loop

EX-2723 kernel: fix potential infinite loop

In dquot_writeback_dquots(), we write back dquot from dirty dquots
list. There is a potential infinite loop if ->write_dquot() failure
and forget remove dquot from the list. This patch clear dirty bit
anyway to avoid it.

Snapshot destroy might dirty quota list, and umount will hang if
filesystem has been mounted as RO because of corrupted image.

Linux-commit: dd5f6279732e8885061d7455b9d86fdcfdf7f183

Change-Id: If5e9db82eacc3a6a621566fb612b55071e51da25
Signed-off-by: zhangyi (F) <yi.zhang@huawei.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Wang Shilong <wshilong@ddn.com>
Reviewed-on: https://review.whamcloud.com/43732
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Wang Shilong <wshilong@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Li Xi <lixi@ddn.com>