Mark BufferedChannelIterator.continuation @BeningDataRace to address potential UB and OoTA on K/N

Fixes #3834

Author: qwwdfsad

kotlinx-coroutines-core/common/src/channels/BufferedChannel.kt

@@ -1583,6 +1583,7 @@ internal open class BufferedChannel<E>(
          * continuation. The [tryResumeHasNext] and [tryResumeHasNextOnClosedChannel]
          * function resume this continuation when the [hasNext] invocation should complete.
          */
+        @BenignDataRace // See its uses for the explanation of the race
         private var continuation: CancellableContinuationImpl<Boolean>? = null
 
         // `hasNext()` is just a special receive operation.

kotlinx-coroutines-core/common/src/internal/Concurrent.common.kt

@@ -12,3 +12,15 @@ internal expect class ReentrantLock() {
 internal expect inline fun <T> ReentrantLock.withLock(action: () -> T): T
 
 internal expect fun <E> identitySet(expectedSize: Int): MutableSet<E>
+
+/**
+ * Annotation indicating that the marked property is the subject of benign data race.
+ * LLVM does not support this notion, so on K/N platforms we alias it into `@Volatile` to prevent potential OoTA.
+ *
+ * The purpose of this annotation is not to save an extra-volatile on JVM platform, but rather to explicitly emphasize
+ * that data-race is benign.
+ */
+@OptionalExpectation
+@Target(AnnotationTarget.FIELD)
+@OptIn(ExperimentalMultiplatform::class)
+internal expect annotation class BenignDataRace()

kotlinx-coroutines-core/native/src/internal/Concurrent.kt

@@ -29,3 +29,5 @@ internal open class SuppressSupportingThrowableImpl : Throwable() {
     }
 }
 
+@Suppress("ACTUAL_WITHOUT_EXPECT") // This suppress can be removed in 2.0: KT-59355
+internal actual typealias BenignDataRace = kotlin.concurrent.Volatile