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 | 62 +++++++++++++++++++++++++++++++++++++++++++++++----
1 file changed, 58 insertions(+), 4 deletions(-)
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 841f9a8..d640865 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 > 0))
+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 +756,16 @@ 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);
--
2.5.0
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