From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S938007AbXHPCt1 (ORCPT ); Wed, 15 Aug 2007 22:49:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932140AbXHPCtM (ORCPT ); Wed, 15 Aug 2007 22:49:12 -0400 Received: from e6.ny.us.ibm.com ([32.97.182.146]:40370 "EHLO e6.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760648AbXHPCtJ (ORCPT ); Wed, 15 Aug 2007 22:49:09 -0400 Date: Wed, 15 Aug 2007 19:49:04 -0700 From: "Paul E. McKenney" To: akpm@linux-foundation.org Cc: bunk@kernel.org, josh@kernel.org, linux-kernel@vger.kernel.org, mingo@elte.hu Subject: [PATCH] Make rcutorture RNG use temporal entropy Message-ID: <20070816024904.GA5312@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Repost of http://lkml.org/lkml/2007/8/10/472 made available by request. The locking used by get_random_bytes() can conflict with the preempt_disable() and synchronize_sched() form of RCU. This patch changes rcutorture's RNG to gather entropy from the new cpu_clock() interface (relying on interrupts, preemption, daemons, and rcutorture's reader thread's rock-bottom scheduling priority to provide useful entropy), and also adds and EXPORT_SYMBOL_GPL() to make that interface available to GPLed kernel modules such as rcutorture. Passes several hours of rcutorture. Signed-off-by: Paul E. McKenney --- rcutorture.c | 8 ++------ sched.c | 2 ++ 2 files changed, 4 insertions(+), 6 deletions(-) diff -urpNa -X dontdiff linux-2.6.23-rc2/kernel/rcutorture.c linux-2.6.23-rc2-rcutorturesched/kernel/rcutorture.c --- linux-2.6.23-rc2/kernel/rcutorture.c 2007-08-03 19:49:55.000000000 -0700 +++ linux-2.6.23-rc2-rcutorturesched/kernel/rcutorture.c 2007-08-10 17:15:22.000000000 -0700 @@ -42,7 +42,6 @@ #include #include #include -#include #include #include #include @@ -166,16 +165,13 @@ struct rcu_random_state { /* * Crude but fast random-number generator. Uses a linear congruential - * generator, with occasional help from get_random_bytes(). + * generator, with occasional help from cpu_clock(). */ static unsigned long rcu_random(struct rcu_random_state *rrsp) { - long refresh; - if (--rrsp->rrs_count < 0) { - get_random_bytes(&refresh, sizeof(refresh)); - rrsp->rrs_state += refresh; + rrsp->rrs_state += (unsigned long)cpu_clock(smp_processor_id()); rrsp->rrs_count = RCU_RANDOM_REFRESH; } rrsp->rrs_state = rrsp->rrs_state * RCU_RANDOM_MULT + RCU_RANDOM_ADD; diff -urpNa -X dontdiff linux-2.6.23-rc2/kernel/sched.c linux-2.6.23-rc2-rcutorturesched/kernel/sched.c --- linux-2.6.23-rc2/kernel/sched.c 2007-08-03 19:49:55.000000000 -0700 +++ linux-2.6.23-rc2-rcutorturesched/kernel/sched.c 2007-08-10 17:22:57.000000000 -0700 @@ -394,6 +394,8 @@ unsigned long long cpu_clock(int cpu) return now; } +EXPORT_SYMBOL_GPL(cpu_clock); + #ifdef CONFIG_FAIR_GROUP_SCHED /* Change a task's ->cfs_rq if it moves across CPUs */ static inline void set_task_cfs_rq(struct task_struct *p)