Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751620AbWHSAt6 (ORCPT ); Fri, 18 Aug 2006 20:49:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751618AbWHSAt6 (ORCPT ); Fri, 18 Aug 2006 20:49:58 -0400 Received: from e2.ny.us.ibm.com ([32.97.182.142]:28546 "EHLO e2.ny.us.ibm.com") by vger.kernel.org with ESMTP id S1751613AbWHSAt5 (ORCPT ); Fri, 18 Aug 2006 20:49:57 -0400 Date: Fri, 18 Aug 2006 17:50:46 -0700 From: "Paul E. McKenney" To: Josh Triplett Cc: linux-kernel@vger.kernel.org, Andrew Morton , Dipkanar Sarma Subject: Re: [PATCH] rcu: Fix sign bug making rcu_random always return the same sequence Message-ID: <20060819005045.GE1317@us.ibm.com> Reply-To: paulmck@us.ibm.com References: <1155947717.5337.9.camel@josh-work.beaverton.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1155947717.5337.9.camel@josh-work.beaverton.ibm.com> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1797 Lines: 48 On Fri, Aug 18, 2006 at 05:35:17PM -0700, Josh Triplett wrote: > rcu_random uses a counter rrs_count to occasionally mix data from > get_random_bytes into the state of its pseudorandom generator. However, the > rrs_counter gets declared as an unsigned long, and rcu_random checks for > --rrs_count < 0, so this code will never mix any real random data into the > state, and will thus always return the same sequence of random numbers. > > Also, change the return value of rcu_random from long to unsigned long, to > avoid potential issues caused by the use of the % operator, which can return > negative values for negative left operands. Acked-by: Paul E. McKenney > Signed-off-by: Josh Triplett > --- > kernel/rcutorture.c | 4 ++-- > 1 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c > index 8b09c95..ef6a124 100644 > --- a/kernel/rcutorture.c > +++ b/kernel/rcutorture.c > @@ -146,7 +146,7 @@ rcu_torture_free(struct rcu_torture *p) > > struct rcu_random_state { > unsigned long rrs_state; > - unsigned long rrs_count; > + long rrs_count; > }; > > #define RCU_RANDOM_MULT 39916801 /* prime */ > @@ -159,7 +159,7 @@ #define DEFINE_RCU_RANDOM(name) struct r > * Crude but fast random-number generator. Uses a linear congruential > * generator, with occasional help from get_random_bytes(). > */ > -static long > +static unsigned long > rcu_random(struct rcu_random_state *rrsp) > { > long refresh; > -- > 1.4.1.1 > > - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/