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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>
This commit is contained in:
Theodore Ts'o 2016-05-02 02:04:41 -04:00
parent e192be9d9a
commit 1e7f583af6
1 changed files with 58 additions and 4 deletions
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62
drivers/char/random.c
View File

@ -436,6 +436,8 @@ static int crng_init = 0;
#define crng_ready() (likely(crng_init > 0))
static int crng_init_cnt = 0;
#define CRNG_INIT_CNT_THRESH (2*CHACHA20_KEY_SIZE)
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);
@ -756,6 +758,16 @@ 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 crng_initialize(struct crng_state *crng)
{
int i;
@ -815,7 +827,7 @@ 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;
@ -835,19 +847,26 @@ 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 > 1 &&
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;
@ -857,6 +876,19 @@ static void extract_crng(__u8 out[CHACHA20_BLOCK_SIZE])
spin_unlock_irqrestore(&crng->lock, flags);
}
static void extract_crng(__u8 out[CHACHA20_BLOCK_SIZE])
{
struct crng_state *crng = NULL;
#ifdef CONFIG_NUMA
if (crng_node_pool)
crng = crng_node_pool[numa_node_id()];
if (crng == NULL)
#endif
crng = &primary_crng;
_extract_crng(crng, out);
}
static ssize_t extract_crng_user(void __user *buf, size_t nbytes)
{
ssize_t ret = 0, i;
@ -1575,9 +1607,31 @@ 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;
struct crng_state **pool;
#endif
init_std_data(&input_pool);
init_std_data(&blocking_pool);
crng_initialize(&primary_crng);
#ifdef CONFIG_NUMA
pool = kmalloc(num_nodes * sizeof(void *),
GFP_KERNEL|__GFP_NOFAIL|__GFP_ZERO);
for (i=0; i < num_nodes; i++) {
crng = kmalloc_node(sizeof(struct crng_state),
GFP_KERNEL | __GFP_NOFAIL, i);
spin_lock_init(&crng->lock);
crng_initialize(crng);
pool[i] = crng;
}
mb();
crng_node_pool = pool;
#endif
return 0;
}
early_initcall(rand_initialize);