Commit c17ac855 authored Oct 16, 2007 by Paul E. McKenney Committed by Linus Torvalds Oct 17, 2007

Make rcutorture RNG use temporal entropy

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.

[ego@in.ibm.com: Use raw_smp_processor_id() in rcu_random()]
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent b2d9323d

kernel/rcutorture.c

+3 −6

Original line number	Diff line number	Diff line
		@@ -41,7 +41,6 @@
		#include <linux/notifier.h>
		#include <linux/freezer.h>
		#include <linux/cpu.h>
		#include <linux/random.h>
		#include <linux/delay.h>
		#include <linux/byteorder/swabb.h>
		#include <linux/stat.h>
		@@ -165,16 +164,14 @@ 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(raw_smp_processor_id());
		rrsp->rrs_count = RCU_RANDOM_REFRESH;
		}
		rrsp->rrs_state = rrsp->rrs_state * RCU_RANDOM_MULT + RCU_RANDOM_ADD;

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