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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2007-10-17 10:27:19 +0400
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-10-17 19:42:53 +0400
commitc17ac85504efec5f3a9b0c5b05bffd6f30e5b655 (patch)
tree8643b155ac0530142f2149ddf590ab08bb03b8c2
parentb2d9323d139f5c384fa1ef1d74773b4db1c09b3d (diff)
downloadlinux-c17ac85504efec5f3a9b0c5b05bffd6f30e5b655.tar.xz
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>
-rw-r--r--kernel/rcutorture.c9
1 files changed, 3 insertions, 6 deletions
diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
index dd413bf6a1d2..c3e165c2318f 100644
--- a/kernel/rcutorture.c
+++ b/kernel/rcutorture.c
@@ -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;