diff options
| -rw-r--r-- | drivers/char/random.c | 52 |
1 files changed, 44 insertions, 8 deletions
diff --git a/drivers/char/random.c b/drivers/char/random.c index 7b71cea6a6ab..3db4bf6f9b43 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -53,6 +53,7 @@ #include <linux/uaccess.h> #include <linux/suspend.h> #include <linux/siphash.h> +#include <linux/sched/isolation.h> #include <crypto/chacha.h> #include <crypto/blake2s.h> #include <asm/processor.h> @@ -1232,7 +1233,8 @@ void __cold rand_initialize_disk(struct gendisk *disk) struct entropy_timer_state { unsigned long entropy; struct timer_list timer; - unsigned int samples, samples_per_bit; + atomic_t samples; + unsigned int samples_per_bit; }; /* @@ -1250,10 +1252,8 @@ static void __cold entropy_timer(struct timer_list *timer) { struct entropy_timer_state *state = container_of(timer, struct entropy_timer_state, timer); - if (++state->samples == state->samples_per_bit) { + if (atomic_inc_return(&state->samples) % state->samples_per_bit == 0) credit_init_bits(1); - state->samples = 0; - } } /* @@ -1266,6 +1266,7 @@ 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(); @@ -1277,19 +1278,54 @@ static void __cold try_to_generate_entropy(void) if (stack.samples_per_bit > MAX_SAMPLES_PER_BIT) return; - stack.samples = 0; + atomic_set(&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); + /* + * Check !timer_pending() and then ensure that any previous callback has finished + * executing by checking try_to_del_timer_sync(), before queueing the next one. + */ + if (!timer_pending(&stack.timer) && try_to_del_timer_sync(&stack.timer) >= 0) { + struct cpumask timer_cpus; + unsigned int num_cpus; + + /* + * Preemption must be disabled here, both to read the current CPU number + * and to avoid scheduling a timer on a dead CPU. + */ + preempt_disable(); + + /* Only schedule callbacks on timer CPUs that are online. */ + cpumask_and(&timer_cpus, housekeeping_cpumask(HK_TYPE_TIMER), cpu_online_mask); + num_cpus = cpumask_weight(&timer_cpus); + /* In very bizarre case of misconfiguration, fallback to all online. */ + if (unlikely(num_cpus == 0)) { + timer_cpus = *cpu_online_mask; + num_cpus = cpumask_weight(&timer_cpus); + } + + /* Basic CPU round-robin, which avoids the current CPU. */ + do { + cpu = cpumask_next(cpu, &timer_cpus); + if (cpu == nr_cpumask_bits) + cpu = cpumask_first(&timer_cpus); + } while (cpu == smp_processor_id() && num_cpus > 1); + + /* Expiring the timer at `jiffies` means it's the next tick. */ + 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(); } + mix_pool_bytes(&stack.entropy, sizeof(stack.entropy)); del_timer_sync(&stack.timer); destroy_timer_on_stack(&stack.timer); - mix_pool_bytes(&stack.entropy, sizeof(stack.entropy)); } |