From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.7 required=3.0 tests=DATE_IN_PAST_96_XX, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5E77BC43331 for ; Sat, 28 Mar 2020 16:43:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3F85D206F6 for ; Sat, 28 Mar 2020 16:43:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727822AbgC1Qnn (ORCPT ); Sat, 28 Mar 2020 12:43:43 -0400 Received: from mx.sdf.org ([205.166.94.20]:50097 "EHLO mx.sdf.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727627AbgC1Qn1 (ORCPT ); Sat, 28 Mar 2020 12:43:27 -0400 Received: from sdf.org (IDENT:lkml@sdf.lonestar.org [205.166.94.16]) by mx.sdf.org (8.15.2/8.14.5) with ESMTPS id 02SGh6Cr021330 (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256 bits) verified NO); Sat, 28 Mar 2020 16:43:07 GMT Received: (from lkml@localhost) by sdf.org (8.15.2/8.12.8/Submit) id 02SGh6ii026355; Sat, 28 Mar 2020 16:43:06 GMT Message-Id: <202003281643.02SGh6ii026355@sdf.org> From: George Spelvin Date: Wed, 4 Dec 2019 00:25:58 -0500 Subject: [RFC PATCH v1 02/50] lib/fault-inject.c: Fix off-by-one error in probability To: linux-kernel@vger.kernel.org, lkml@sdf.org Cc: Akinobu Mita , Anton Blanchard Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is the combination of two fixes. First, use prandom_u32_max() for efficiency: - if (attr->probability <= prandom_u32() % 100) + if (attr->probability <= prandom_u32_max(100)) return false And then a bug-fix: - if (attr->probability <= prandom_u32_max(100)) + if (attr->probability < prandom_u32_max(100)) return false Before, probability = 1 would succeed 2% of the time and 99 would succeed 100% of the time. (0% was caught by an earlier test.) Signed-off-by: George Spelvin Cc: Akinobu Mita Cc: Anton Blanchard --- lib/fault-inject.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/lib/fault-inject.c b/lib/fault-inject.c index 8186ca84910bc..e20151fa5515e 100644 --- a/lib/fault-inject.c +++ b/lib/fault-inject.c @@ -134,7 +134,7 @@ bool should_fail(struct fault_attr *attr, ssize_t size) return false; } - if (attr->probability <= prandom_u32() % 100) + if (attr->probability < prandom_u32_max(100)) return false; if (!fail_stacktrace(attr)) -- 2.26.0