random: move initialization out of reseeding hot path

Initialization happens once -- by way of credit_init_bits() -- and then
it never happens again. Therefore, it doesn't need to be in
crng_reseed(), which is a hot path that is called multiple times. It
also doesn't make sense to have there, as initialization activity is
better associated with initialization routines.

After the prior commit, crng_reseed() now won't be called by multiple
concurrent callers, which means that we can safely move the
"finialize_init" logic into crng_init_bits() unconditionally.

Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 8b451e8490b52bccda67afaf65237359ffb0ea78..07200b8f459136992b5afa495b10fa8eaa67a154 100644 (file)
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -265,7 +265,6 @@ static void crng_reseed(void)
        unsigned long flags;
        unsigned long next_gen;
        u8 key[CHACHA_KEY_SIZE];
-       bool finalize_init = false;
 
        extract_entropy(key, sizeof(key));
 
@@ -282,28 +281,10 @@ static void crng_reseed(void)
                ++next_gen;
        WRITE_ONCE(base_crng.generation, next_gen);
        WRITE_ONCE(base_crng.birth, jiffies);
-       if (!crng_ready()) {
+       if (!crng_ready())
                crng_init = CRNG_READY;
-               finalize_init = true;
-       }
        spin_unlock_irqrestore(&base_crng.lock, flags);
        memzero_explicit(key, sizeof(key));
-       if (finalize_init) {
-               process_random_ready_list();
-               wake_up_interruptible(&crng_init_wait);
-               kill_fasync(&fasync, SIGIO, POLL_IN);
-               pr_notice("crng init done\n");
-               if (unseeded_warning.missed) {
-                       pr_notice("%d get_random_xx warning(s) missed due to ratelimiting\n",
-                                 unseeded_warning.missed);
-                       unseeded_warning.missed = 0;
-               }
-               if (urandom_warning.missed) {
-                       pr_notice("%d urandom warning(s) missed due to ratelimiting\n",
-                                 urandom_warning.missed);
-                       urandom_warning.missed = 0;
-               }
-       }
 }
 
 /*
@@ -835,10 +816,25 @@ static void credit_init_bits(size_t nbits)
                new = min_t(unsigned int, POOL_BITS, orig + add);
        } while (cmpxchg(&input_pool.init_bits, orig, new) != orig);
 
-       if (orig < POOL_READY_BITS && new >= POOL_READY_BITS)
-               crng_reseed();
-       else if (orig < POOL_EARLY_BITS && new >= POOL_EARLY_BITS) {
+       if (orig < POOL_READY_BITS && new >= POOL_READY_BITS) {
+               crng_reseed(); /* Sets crng_init to CRNG_READY under base_crng.lock. */
+               process_random_ready_list();
+               wake_up_interruptible(&crng_init_wait);
+               kill_fasync(&fasync, SIGIO, POLL_IN);
+               pr_notice("crng init done\n");
+               if (unseeded_warning.missed) {
+                       pr_notice("%d get_random_xx warning(s) missed due to ratelimiting\n",
+                                 unseeded_warning.missed);
+                       unseeded_warning.missed = 0;
+               }
+               if (urandom_warning.missed) {
+                       pr_notice("%d urandom warning(s) missed due to ratelimiting\n",
+                                 urandom_warning.missed);
+                       urandom_warning.missed = 0;
+               }
+       } else if (orig < POOL_EARLY_BITS && new >= POOL_EARLY_BITS) {
                spin_lock_irqsave(&base_crng.lock, flags);
+               /* Check if crng_init is CRNG_EMPTY, to avoid race with crng_reseed(). */
                if (crng_init == CRNG_EMPTY) {
                        extract_entropy(base_crng.key, sizeof(base_crng.key));
                        crng_init = CRNG_EARLY;