f2fs: prevent waiter encountering incorrect discard states

In f2fs_submit_discard_endio, we will wake up waiter before setting
discard command states, so waiter may use incorrect states. Change
the order between complete() and states setting to fix this issue.
Signed-off-by: NChao Yu <yuchao0@huawei.com>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/segment.c

@@ -717,9 +717,9 @@ static void f2fs_submit_discard_endio(struct bio *bio)
 {
 	struct discard_cmd *dc = (struct discard_cmd *)bio->bi_private;
 
-	complete(&dc->wait);
 	dc->error = bio->bi_error;
 	dc->state = D_DONE;
+	complete(&dc->wait);
 	bio_put(bio);
 }
 
@@ -807,8 +807,7 @@ void f2fs_wait_discard_bio(struct f2fs_sb_info *sbi, block_t blkaddr)
 
 	list_for_each_entry_safe(dc, tmp, wait_list, list) {
 		if (dc->lstart <= blkaddr && blkaddr < dc->lstart + dc->len) {
-			if (dc->state == D_SUBMIT)
-				wait_for_completion_io(&dc->wait);
+			wait_for_completion_io(&dc->wait);
 			__punch_discard_cmd(sbi, dc, blkaddr);
 		}
 	}
@@ -868,8 +867,10 @@ static int issue_discard_thread(void *data)
 	}
 
 	list_for_each_entry_safe(dc, tmp, wait_list, list) {
-		if (dc->state == D_DONE)
+		if (dc->state == D_DONE) {
+			wait_for_completion_io(&dc->wait);
 			__remove_discard_cmd(sbi, dc);
+		}
 	}
 	mutex_unlock(&dcc->cmd_lock);