random: make /dev/urandom scalable for silly userspace programs
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@linux.intel.com> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
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@ -436,6 +436,8 @@ static int crng_init = 0;
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#define crng_ready() (likely(crng_init > 0))
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static int crng_init_cnt = 0;
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#define CRNG_INIT_CNT_THRESH (2*CHACHA20_KEY_SIZE)
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static void _extract_crng(struct crng_state *crng,
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__u8 out[CHACHA20_BLOCK_SIZE]);
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static void extract_crng(__u8 out[CHACHA20_BLOCK_SIZE]);
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static void process_random_ready_list(void);
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@ -756,6 +758,16 @@ static void credit_entropy_bits_safe(struct entropy_store *r, int nbits)
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static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait);
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#ifdef CONFIG_NUMA
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/*
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* Hack to deal with crazy userspace progams when they are all trying
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* to access /dev/urandom in parallel. The programs are almost
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* certainly doing something terribly wrong, but we'll work around
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* their brain damage.
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*/
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static struct crng_state **crng_node_pool __read_mostly;
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#endif
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static void crng_initialize(struct crng_state *crng)
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{
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int i;
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@ -815,7 +827,7 @@ static void crng_reseed(struct crng_state *crng, struct entropy_store *r)
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if (num == 0)
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return;
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} else
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extract_crng(buf.block);
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_extract_crng(&primary_crng, buf.block);
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spin_lock_irqsave(&primary_crng.lock, flags);
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for (i = 0; i < 8; i++) {
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unsigned long rv;
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@ -835,19 +847,26 @@ static void crng_reseed(struct crng_state *crng, struct entropy_store *r)
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spin_unlock_irqrestore(&primary_crng.lock, flags);
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}
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static inline void maybe_reseed_primary_crng(void)
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{
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if (crng_init > 2 &&
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time_after(jiffies, primary_crng.init_time + CRNG_RESEED_INTERVAL))
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crng_reseed(&primary_crng, &input_pool);
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}
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static inline void crng_wait_ready(void)
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{
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wait_event_interruptible(crng_init_wait, crng_ready());
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}
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static void extract_crng(__u8 out[CHACHA20_BLOCK_SIZE])
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static void _extract_crng(struct crng_state *crng,
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__u8 out[CHACHA20_BLOCK_SIZE])
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{
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unsigned long v, flags;
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struct crng_state *crng = &primary_crng;
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if (crng_init > 1 &&
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time_after(jiffies, crng->init_time + CRNG_RESEED_INTERVAL))
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crng_reseed(crng, &input_pool);
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crng_reseed(crng, crng == &primary_crng ? &input_pool : NULL);
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spin_lock_irqsave(&crng->lock, flags);
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if (arch_get_random_long(&v))
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crng->state[14] ^= v;
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@ -857,6 +876,19 @@ static void extract_crng(__u8 out[CHACHA20_BLOCK_SIZE])
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spin_unlock_irqrestore(&crng->lock, flags);
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}
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static void extract_crng(__u8 out[CHACHA20_BLOCK_SIZE])
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{
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struct crng_state *crng = NULL;
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#ifdef CONFIG_NUMA
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if (crng_node_pool)
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crng = crng_node_pool[numa_node_id()];
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if (crng == NULL)
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#endif
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crng = &primary_crng;
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_extract_crng(crng, out);
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}
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static ssize_t extract_crng_user(void __user *buf, size_t nbytes)
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{
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ssize_t ret = 0, i;
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@ -1575,9 +1607,31 @@ static void init_std_data(struct entropy_store *r)
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*/
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static int rand_initialize(void)
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{
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#ifdef CONFIG_NUMA
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int i;
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int num_nodes = num_possible_nodes();
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struct crng_state *crng;
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struct crng_state **pool;
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#endif
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init_std_data(&input_pool);
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init_std_data(&blocking_pool);
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crng_initialize(&primary_crng);
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#ifdef CONFIG_NUMA
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pool = kmalloc(num_nodes * sizeof(void *),
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GFP_KERNEL|__GFP_NOFAIL|__GFP_ZERO);
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for (i=0; i < num_nodes; i++) {
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crng = kmalloc_node(sizeof(struct crng_state),
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GFP_KERNEL | __GFP_NOFAIL, i);
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spin_lock_init(&crng->lock);
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crng_initialize(crng);
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pool[i] = crng;
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}
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mb();
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crng_node_pool = pool;
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#endif
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return 0;
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}
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early_initcall(rand_initialize);
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