f2fs: avoid null pointer exception in dcc_info

If dcc_info is not set yet, we can get null pointer panic.
Reviewed-by: NChao Yu <yuchao0@huawei.com>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/f2fs.h

@@ -2161,10 +2161,17 @@ static inline bool is_idle(struct f2fs_sb_info *sbi, int type)
 		get_pages(sbi, F2FS_RD_META) || get_pages(sbi, F2FS_WB_DATA) ||
 		get_pages(sbi, F2FS_WB_CP_DATA) ||
 		get_pages(sbi, F2FS_DIO_READ) ||
-		get_pages(sbi, F2FS_DIO_WRITE) ||
-		atomic_read(&SM_I(sbi)->dcc_info->queued_discard) ||
-		atomic_read(&SM_I(sbi)->fcc_info->queued_flush))
+		get_pages(sbi, F2FS_DIO_WRITE))
 		return false;
+
+	if (SM_I(sbi) && SM_I(sbi)->dcc_info &&
+			atomic_read(&SM_I(sbi)->dcc_info->queued_discard))
+		return false;
+
+	if (SM_I(sbi) && SM_I(sbi)->fcc_info &&
+			atomic_read(&SM_I(sbi)->fcc_info->queued_flush))
+		return false;
+
 	return f2fs_time_over(sbi, type);
 }