f2fs: fix to avoid long latency during umount

In umount, we give an constand time to handle pending discard, previously,
in __issue_discard_cmd() we missed to check timeout condition in loop,
result in delaying long time, fix it.

Signed-off-by: Heng Xiao <heng.xiao@unisoc.com>
[Chao Yu: add commit message]
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/segment.c

@@ -1497,6 +1497,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
 		list_for_each_entry_safe(dc, tmp, pend_list, list) {
 			f2fs_bug_on(sbi, dc->state != D_PREP);
 
+			if (dpolicy->timeout != 0 &&
+				f2fs_time_over(sbi, dpolicy->timeout))
+				break;
+
 			if (dpolicy->io_aware && i < dpolicy->io_aware_gran &&
 						!is_idle(sbi, DISCARD_TIME)) {
 				io_interrupted = true;