Am Montag, 30. Mai 2016, 01:39:22 schrieb Theodore Ts'o:
Hi Theodore,
> On a system with a 4 socket (NUMA) system where a large number of
> application threads were all trying to read from /dev/urandom, this
> can result in the system spending 80% of its time contending on the
> global urandom spinlock. The application should have used its own
> PRNG, but let's try to help it from running, lemming-like, straight
> over the locking cliff.
>
> Reported-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
> ---
> drivers/char/random.c | 57
> +++++++++++++++++++++++++++++++++++++++++++++++---- 1 file changed, 53
> insertions(+), 4 deletions(-)
>
> diff --git a/drivers/char/random.c b/drivers/char/random.c
> index 3a4d865..1778c84 100644
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -434,6 +434,8 @@ struct crng_state primary_crng = {
> */
> static int crng_init = 0;
> #define crng_ready() (likely(crng_init >= 2))
> +static void _extract_crng(struct crng_state *crng,
> + __u8 out[CHACHA20_BLOCK_SIZE]);
> static void extract_crng(__u8 out[CHACHA20_BLOCK_SIZE]);
> static void process_random_ready_list(void);
>
> @@ -754,6 +756,17 @@ static void credit_entropy_bits_safe(struct
> entropy_store *r, int nbits)
>
> static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait);
>
> +#ifdef CONFIG_NUMA
> +/*
> + * Hack to deal with crazy userspace progams when they are all trying
> + * to access /dev/urandom in parallel. The programs are almost
> + * certainly doing something terribly wrong, but we'll work around
> + * their brain damage.
> + */
> +static struct crng_state **crng_node_pool __read_mostly;
> +#endif
> +
> +
> static void _initialize_crng(struct crng_state *crng)
> {
> int i;
> @@ -774,11 +787,13 @@ static void _initialize_crng(struct crng_state *crng)
> crng->init_time = jiffies - CRNG_RESEED_INTERVAL - 1;
> }
>
> +#ifdef CONFIG_NUMA
> static void initialize_crng(struct crng_state *crng)
> {
> _initialize_crng(crng);
> spin_lock_init(&crng->lock);
> }
> +#endif
>
> static int crng_fast_load(__u32 pool[4])
> {
> @@ -818,7 +833,7 @@ static void crng_reseed(struct crng_state *crng, struct
> entropy_store *r) if (num == 0)
> return;
> } else
> - extract_crng(buf.block);
> + _extract_crng(&primary_crng, buf.block);
> spin_lock_irqsave(&primary_crng.lock, flags);
> for (i = 0; i < 8; i++) {
> unsigned long rv;
> @@ -838,19 +853,26 @@ static void crng_reseed(struct crng_state *crng,
> struct entropy_store *r) spin_unlock_irqrestore(&primary_crng.lock, flags);
> }
>
> +static inline void maybe_reseed_primary_crng(void)
> +{
> + if (crng_init > 2 &&
> + time_after(jiffies, primary_crng.init_time +
CRNG_RESEED_INTERVAL))
> + crng_reseed(&primary_crng, &input_pool);
> +}
> +
> static inline void crng_wait_ready(void)
> {
> wait_event_interruptible(crng_init_wait, crng_ready());
> }
>
> -static void extract_crng(__u8 out[CHACHA20_BLOCK_SIZE])
> +static void _extract_crng(struct crng_state *crng,
> + __u8 out[CHACHA20_BLOCK_SIZE])
> {
> unsigned long v, flags;
> - struct crng_state *crng = &primary_crng;
>
> if (crng_init > 2 &&
> time_after(jiffies, crng->init_time + CRNG_RESEED_INTERVAL))
> - crng_reseed(crng, &input_pool);
> + crng_reseed(crng, crng == &primary_crng ? &input_pool : NULL);
> spin_lock_irqsave(&crng->lock, flags);
> if (arch_get_random_long(&v))
> crng->state[14] ^= v;
> @@ -860,6 +882,17 @@ static void extract_crng(__u8 out[CHACHA20_BLOCK_SIZE])
> spin_unlock_irqrestore(&crng->lock, flags);
> }
>
> +static void extract_crng(__u8 out[CHACHA20_BLOCK_SIZE])
> +{
> +#ifndef CONFIG_NUMA
> + struct crng_state *crng = &primary_crng;
> +#else
> + struct crng_state *crng = crng_node_pool[numa_node_id()];
> +#endif
> +
> + _extract_crng(crng, out);
> +}
> +
> static ssize_t extract_crng_user(void __user *buf, size_t nbytes)
> {
> ssize_t ret = 0, i;
> @@ -1573,6 +1606,22 @@ static void init_std_data(struct entropy_store *r)
> */
> static int rand_initialize(void)
> {
> +#ifdef CONFIG_NUMA
> + int i;
> + int num_nodes = num_possible_nodes();
> + struct crng_state *crng;
> +
> + crng_node_pool = kmalloc(num_nodes * sizeof(void *),
> + GFP_KERNEL|__GFP_NOFAIL);
> +
> + for (i=0; i < num_nodes; i++) {
> + crng = kmalloc(sizeof(struct crng_state),
> + GFP_KERNEL | __GFP_NOFAIL);
> + initialize_crng(crng);
Could you please help me understand the logic flow here: The NUMA secondary
DRNGs are initialized before the input/blocking pools and the primary DRNG.
The initialization call uses get_random_bytes() for the secondary DRNGs. But
since the primary DRNG is not yet initialized, where does the get_random_bytes
gets its randomness from?
> + crng_node_pool[i] = crng;
> +
> + }
> +#endif
> init_std_data(&input_pool);
> init_std_data(&blocking_pool);
> _initialize_crng(&primary_crng);
Ciao
Stephan
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