@@ -1209,6 +1209,7 @@ static void __cold try_to_generate_entropy(void)
struct entropy_timer_state stack;
unsigned int i, num_different = 0;
unsigned long last = random_get_entropy();
+ int cpu = -1;
for (i = 0; i < NUM_TRIAL_SAMPLES - 1; ++i) {
stack.entropy = random_get_entropy();
@@ -1223,8 +1224,17 @@ static void __cold try_to_generate_entropy(void)
stack.samples = 0;
timer_setup_on_stack(&stack.timer, entropy_timer, 0);
while (!crng_ready() && !signal_pending(current)) {
- if (!timer_pending(&stack.timer))
- mod_timer(&stack.timer, jiffies);
+ if (!timer_pending(&stack.timer)) {
+ preempt_disable();
+ do {
+ cpu = cpumask_next(cpu, cpu_online_mask);
+ if (cpu == nr_cpumask_bits)
+ cpu = cpumask_first(cpu_online_mask);
+ } while (cpu == smp_processor_id() && cpumask_weight(cpu_online_mask) > 1);
+ stack.timer.expires = jiffies;
+ add_timer_on(&stack.timer, cpu);
+ preempt_enable();
+ }
mix_pool_bytes(&stack.entropy, sizeof(stack.entropy));
schedule();
stack.entropy = random_get_entropy();
Rather than merely hoping that the callback gets called on another CPU, arrange for that to actually happen, by round robining which CPU the timer fires on. This way, on multiprocessor machines, we exacerbate jitter by touching the same memory from multiple different cores. Cc: Dominik Brodowski <linux@dominikbrodowski.net> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: Sultan Alsawaf <sultan@kerneltoast.com> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> --- drivers/char/random.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-)