[dev.boringcrypto] all: merge master into dev.boringcrypto

Change-Id: I30dbbe508a6252d50b4154cb9a8299cf0a054449

diff --cc src/crypto/rand/rand_unix.go
index 0b137e131f0142b50b6082cc4b39168080bab3db,07715bd5ee02662dac715fdbd9817746cfb2c1d0..87ba9e3af7aaa8bf601fab3f997d54e5beef794b
--- 1/src/crypto/rand/rand_unix.go
--- 2/src/crypto/rand/rand_unix.go
+++ b/src/crypto/rand/rand_unix.go
@@@ -94,11 -59,7 +65,8 @@@ func warnBlocked() 
  }
  
  func (r *reader) Read(b []byte) (n int, err error) {
-       r.mu.Lock()
-       defer r.mu.Unlock()
-       if !r.used {
-               r.used = true
 +      boring.Unreachable()
+       if atomic.CompareAndSwapUint32(&r.used, 0, 1) {
                // First use of randomness. Start timer to warn about
                // being blocked on entropy not being available.
                t := time.AfterFunc(time.Minute, warnBlocked)