From: "Paul E. McKenney" 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. Signed-off-by: Paul E. McKenney Cc: Ingo Molnar Signed-off-by: Andrew Morton --- kernel/rcutorture.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-) diff -puN kernel/rcutorture.c~make-rcutorture-rng-use-temporal-entropy kernel/rcutorture.c --- a/kernel/rcutorture.c~make-rcutorture-rng-use-temporal-entropy +++ a/kernel/rcutorture.c @@ -41,7 +41,6 @@ #include #include #include -#include #include #include #include @@ -165,16 +164,13 @@ 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(smp_processor_id()); rrsp->rrs_count = RCU_RANDOM_REFRESH; } rrsp->rrs_state = rrsp->rrs_state * RCU_RANDOM_MULT + RCU_RANDOM_ADD; _