rust: sync: Use safe synchronize_rcu() abstraction in poll

We now have a safe wrapper for the foreign function synchronize_rcu().

Use it in poll.rs.

Signed-off-by: Philipp Stanner <phasta@kernel.org>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Onur Özkan <work@onurozkan.dev>
Reviewed-by: Danilo Krummrich <dakr@kernel.org>
Reviewed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Boqun Feng <boqun@kernel.org>
Link: https://patch.msgid.link/20260624150704.1504001-5-phasta@kernel.org

rust/kernel/sync/poll.rs

@@ -8,7 +8,11 @@
     bindings,
     fs::File,
     prelude::*,
-    sync::{CondVar, LockClassKey},
+    sync::{
+        rcu::synchronize_rcu,
+        CondVar,
+        LockClassKey, //
+    }, //
 };
 use core::{marker::PhantomData, ops::Deref};
 
@@ -99,8 +103,6 @@ fn drop(self: Pin<&mut Self>) {
         unsafe { bindings::__wake_up_pollfree(self.inner.wait_queue_head.get()) };
 
         // Wait for epoll items to be properly removed.
-        //
-        // SAFETY: Just an FFI call.
-        unsafe { bindings::synchronize_rcu() };
+        synchronize_rcu();
     }
 }