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>

1 files changed, 58 insertions, 4 deletions

diff --git a/drivers/char/random.c b/drivers/char/random.c
index dc2a9c2d8dcf..2a30d9718a1b 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -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);