random: optimize spinlock use in add_device_randomness()

The add_device_randomness() function calls mix_pool_bytes() twice for
the input pool and the non-blocking pool, for a total of four times.
By using _mix_pool_byte() and taking the spinlock in
add_device_randomness(), we can halve the number of times we need
take each pool's spinlock.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 10 insertions, 4 deletions

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 80b58774e891..89eb5a8dec82 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -710,12 +710,18 @@ struct timer_rand_state {
 void add_device_randomness(const void *buf, unsigned int size)
 {
         unsigned long time = random_get_entropy() ^ jiffies;
+        unsigned long flags;
 
         trace_add_device_randomness(size, _RET_IP_);
-        mix_pool_bytes(&input_pool, buf, size, NULL);
-        mix_pool_bytes(&input_pool, &time, sizeof(time), NULL);
-        mix_pool_bytes(&nonblocking_pool, buf, size, NULL);
-        mix_pool_bytes(&nonblocking_pool, &time, sizeof(time), NULL);
+        spin_lock_irqsave(&input_pool.lock, flags);
+        _mix_pool_bytes(&input_pool, buf, size, NULL);
+        _mix_pool_bytes(&input_pool, &time, sizeof(time), NULL);
+        spin_unlock_irqrestore(&input_pool.lock, flags);
+
+        spin_lock_irqsave(&nonblocking_pool.lock, flags);
+        _mix_pool_bytes(&nonblocking_pool, buf, size, NULL);
+        _mix_pool_bytes(&nonblocking_pool, &time, sizeof(time), NULL);
+        spin_unlock_irqrestore(&nonblocking_pool.lock, flags);
 }
 EXPORT_SYMBOL(add_device_randomness);