From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755830AbcHSH0n (ORCPT ); Fri, 19 Aug 2016 03:26:43 -0400 Received: from mx2.suse.de ([195.135.220.15]:49729 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755039AbcHSHL4 (ORCPT ); Fri, 19 Aug 2016 03:11:56 -0400 X-Amavis-Alert: BAD HEADER SECTION, Duplicate header field: "References" From: Jiri Slaby To: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Daniel Borkmann , Jakub Zawadzki , Eric Dumazet , Hannes Frederic Sowa , "David S . Miller" , Jiri Slaby Subject: [PATCH 3.12 046/100] random32: add prandom_u32_max and convert open coded users Date: Fri, 19 Aug 2016 09:10:45 +0200 Message-Id: <04286471d219e4c8868210dbb069c0b28c17b227.1471589700.git.jslaby@suse.cz> X-Mailer: git-send-email 2.9.3 In-Reply-To: References: In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Daniel Borkmann 3.12-stable review patch. If anyone has any objections, please let me know. =============== commit f337db64af059c9a94278a8b0ab97d87259ff62f upstream. Many functions have open coded a function that returns a random number in range [0,N-1]. Under the assumption that we have a PRNG such as taus113 with being well distributed in [0, ~0U] space, we can implement such a function as uword t = (n*m')>>32, where m' is a random number obtained from PRNG, n the right open interval border and t our resulting random number, with n,m',t in u32 universe. Lets go with Joe and simply call it prandom_u32_max(), although technically we have an right open interval endpoint, but that we have documented. Other users can further be migrated to the new prandom_u32_max() function later on; for now, we need to make sure to migrate reciprocal_divide() users for the reciprocal_divide() follow-up fixup since their function signatures are going to change. Joint work with Hannes Frederic Sowa. Cc: Jakub Zawadzki Cc: Eric Dumazet Cc: linux-kernel@vger.kernel.org Signed-off-by: Hannes Frederic Sowa Signed-off-by: Daniel Borkmann Signed-off-by: David S. Miller Signed-off-by: Jiri Slaby --- drivers/net/team/team_mode_random.c | 8 +------- include/linux/random.h | 18 +++++++++++++++++- net/packet/af_packet.c | 2 +- net/sched/sch_choke.c | 9 +-------- 4 files changed, 20 insertions(+), 17 deletions(-) diff --git a/drivers/net/team/team_mode_random.c b/drivers/net/team/team_mode_random.c index 7f032e211343..cd2f692b8074 100644 --- a/drivers/net/team/team_mode_random.c +++ b/drivers/net/team/team_mode_random.c @@ -13,20 +13,14 @@ #include #include #include -#include #include -static u32 random_N(unsigned int N) -{ - return reciprocal_divide(prandom_u32(), N); -} - static bool rnd_transmit(struct team *team, struct sk_buff *skb) { struct team_port *port; int port_index; - port_index = random_N(team->en_port_count); + port_index = prandom_u32_max(team->en_port_count); port = team_get_port_by_index_rcu(team, port_index); if (unlikely(!port)) goto drop; diff --git a/include/linux/random.h b/include/linux/random.h index bf9085e89fb5..230040642bea 100644 --- a/include/linux/random.h +++ b/include/linux/random.h @@ -8,7 +8,6 @@ #include - extern void add_device_randomness(const void *, unsigned int); extern void add_input_randomness(unsigned int type, unsigned int code, unsigned int value); @@ -33,6 +32,23 @@ void prandom_seed(u32 seed); u32 prandom_u32_state(struct rnd_state *); void prandom_bytes_state(struct rnd_state *state, void *buf, int nbytes); +/** + * prandom_u32_max - returns a pseudo-random number in interval [0, ep_ro) + * @ep_ro: right open interval endpoint + * + * Returns a pseudo-random number that is in interval [0, ep_ro). Note + * that the result depends on PRNG being well distributed in [0, ~0U] + * u32 space. Here we use maximally equidistributed combined Tausworthe + * generator, that is, prandom_u32(). This is useful when requesting a + * random index of an array containing ep_ro elements, for example. + * + * Returns: pseudo-random number in interval [0, ep_ro) + */ +static inline u32 prandom_u32_max(u32 ep_ro) +{ + return (u32)(((u64) prandom_u32() * ep_ro) >> 32); +} + /* * Handle minimum values for seeds */ diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index 63d0f92f45d0..1e9cb9921daa 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -1178,7 +1178,7 @@ static unsigned int fanout_demux_rnd(struct packet_fanout *f, struct sk_buff *skb, unsigned int num) { - return reciprocal_divide(prandom_u32(), num); + return prandom_u32_max(num); } static unsigned int fanout_demux_rollover(struct packet_fanout *f, diff --git a/net/sched/sch_choke.c b/net/sched/sch_choke.c index ddd73cb2d7ba..2aee02802c27 100644 --- a/net/sched/sch_choke.c +++ b/net/sched/sch_choke.c @@ -14,7 +14,6 @@ #include #include #include -#include #include #include #include @@ -77,12 +76,6 @@ struct choke_sched_data { struct sk_buff **tab; }; -/* deliver a random number between 0 and N - 1 */ -static u32 random_N(unsigned int N) -{ - return reciprocal_divide(prandom_u32(), N); -} - /* number of elements in queue including holes */ static unsigned int choke_len(const struct choke_sched_data *q) { @@ -233,7 +226,7 @@ static struct sk_buff *choke_peek_random(const struct choke_sched_data *q, int retrys = 3; do { - *pidx = (q->head + random_N(choke_len(q))) & q->tab_mask; + *pidx = (q->head + prandom_u32_max(choke_len(q))) & q->tab_mask; skb = q->tab[*pidx]; if (skb) return skb; -- 2.9.3