libbinder: update getCallingPid docs

Bug: 297833427
Test: N/A
Change-Id: I406d2dbe68e79fa642df86f979a3f2332a4014bb
diff --git a/libs/binder/rust/src/state.rs b/libs/binder/rust/src/state.rs
index a3a2562..8a06274 100644
--- a/libs/binder/rust/src/state.rs
+++ b/libs/binder/rust/src/state.rs
@@ -101,13 +101,16 @@
     /// dies and is replaced with another process with elevated permissions and
     /// the same PID.
     ///
+    /// Warning: oneway transactions do not receive PID. Even if you expect
+    /// a transaction to be synchronous, a misbehaving client could send it
+    /// as a synchronous call and result in a 0 PID here. Additionally, if
+    /// there is a race and the calling process dies, the PID may still be
+    /// 0 for a synchronous call.
+    ///
     /// Available since API level 29.
     ///
     /// \return calling pid or the current process's PID if this thread isn't
     /// processing a transaction.
-    ///
-    /// If the transaction being processed is a oneway transaction, then this
-    /// method will return 0.
     pub fn get_calling_pid() -> pid_t {
         // Safety: Safe FFI
         unsafe { sys::AIBinder_getCallingPid() }