linux-kernel - [PATCH] batman-adv: fix random jitter calculation

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Message-Id: <1356525130-2688-1-git-send-email-akinobu.mita@gmail.com>
Date:	Wed, 26 Dec 2012 21:32:10 +0900
From:	Akinobu Mita <akinobu.mita@...il.com>
To:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Cc:	Akinobu Mita <akinobu.mita@...il.com>,
	Marek Lindner <lindner_marek@...oo.de>,
	Simon Wunderlich <siwu@....tu-chemnitz.de>,
	Antonio Quartulli <ordex@...istici.org>,
	b.a.t.m.a.n@...ts.open-mesh.org,
	"David S. Miller" <davem@...emloft.net>
Subject: [PATCH] batman-adv: fix random jitter calculation

batadv_iv_ogm_emit_send_time() attempts to calculates a random integer
in the range of 'orig_interval +- BATADV_JITTER' by the below lines.

        msecs = atomic_read(&bat_priv->orig_interval) - BATADV_JITTER;
        msecs += (random32() % 2 * BATADV_JITTER);

But it actually gets 'orig_interval' or 'orig_interval - BATADV_JITTER'
because '%' and '*' have same precedence and associativity is
left-to-right.

This adds the parentheses at the appropriate position so that it matches
original intension.

Signed-off-by: Akinobu Mita <akinobu.mita@...il.com>
Acked-by: Antonio Quartulli <ordex@...istici.org>
Cc: Marek Lindner <lindner_marek@...oo.de>
Cc: Simon Wunderlich <siwu@....tu-chemnitz.de>
Cc: Antonio Quartulli <ordex@...istici.org>
Cc: b.a.t.m.a.n@...ts.open-mesh.org
Cc: "David S. Miller" <davem@...emloft.net>
Cc: netdev@...r.kernel.org
---

This patch is extracted from the patch series "rename random32 and
net_random to prandom" since it is a fix.

 net/batman-adv/bat_iv_ogm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/batman-adv/bat_iv_ogm.c b/net/batman-adv/bat_iv_ogm.c
index 9f3925a..7d02ebd 100644
--- a/net/batman-adv/bat_iv_ogm.c
+++ b/net/batman-adv/bat_iv_ogm.c
@@ -123,7 +123,7 @@ batadv_iv_ogm_emit_send_time(const struct batadv_priv *bat_priv)
 	unsigned int msecs;
 
 	msecs = atomic_read(&bat_priv->orig_interval) - BATADV_JITTER;
-	msecs += (random32() % 2 * BATADV_JITTER);
+	msecs += random32() % (2 * BATADV_JITTER);
 
 	return jiffies + msecs_to_jiffies(msecs);
 }
-- 
1.7.11.7

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