On Mon, Sep 16, 2024 at 12:24 AM Gary Guo [off-list ref] wrote:

On Sun, 15 Sep 2024 14:31:34 +0000
Alice Ryhl [off-list ref] wrote:

quoted

+    /// Register this [`PollTable`] with the provided [`PollCondVar`], so that it can be notified
+    /// using the condition variable.
+    pub fn register_wait(&mut self, file: &File, cv: &PollCondVar) {
+        if let Some(qproc) = self.get_qproc() {
+            // SAFETY: The pointers to `file` and `self` need to be valid for the duration of this
+            // call to `qproc`, which they are because they are references.
+            //
+            // The `cv.wait_queue_head` pointer must be valid until an rcu grace period after the
+            // waiter is removed. The `PollCondVar` is pinned, so before `cv.wait_queue_head` can
+            // be destroyed, the destructor must run. That destructor first removes all waiters,
+            // and then waits for an rcu grace period. Therefore, `cv.wait_queue_head` is valid for
+            // long enough.
+            unsafe { qproc(file.as_ptr() as _, cv.wait_queue_head.get(), self.0.get()) };
+        }

Should this be calling `poll_wait` instead?

quoted

+#[pinned_drop]
+impl PinnedDrop for PollCondVar {
+    fn drop(self: Pin<&mut Self>) {
+        // Clear anything registered using `register_wait`.
+        //
+        // SAFETY: The pointer points at a valid `wait_queue_head`.
+        unsafe { bindings::__wake_up_pollfree(self.inner.wait_queue_head.get()) };

Should this use `wake_up_pollfree` (without the leading __)?

For both cases, that would require a Rust helper. But I suppose we could do it.

Alice