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fix(ffi): fix deadlock in hyper_executor::poll_next (#3370)
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poll_next locks the driver, and also calls drain_queue while holding
that lock. Since drain_queue locks the driver too, that results in a
deadlock.

To fix, unlock the driver before calling drain_queue.

Closes #3369
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jsha authored Oct 23, 2023
1 parent 54c8670 commit 0c7d03e
Showing 1 changed file with 25 additions and 17 deletions.
42 changes: 25 additions & 17 deletions src/ffi/task.rs
Original file line number Diff line number Diff line change
Expand Up @@ -126,27 +126,35 @@ impl hyper_executor {
let mut cx = Context::from_waker(&waker);

loop {
match Pin::new(&mut *self.driver.lock().unwrap()).poll_next(&mut cx) {
Poll::Ready(val) => return val,
Poll::Pending => {
// Check if any of the pending tasks tried to spawn
// some new tasks. If so, drain into the driver and loop.
if self.drain_queue() {
continue;
}

// If the driver called `wake` while we were polling,
// we should poll again immediately!
if self.is_woken.0.swap(false, Ordering::SeqCst) {
continue;
}

return None;
}
{
// Scope the lock on the driver to ensure it is dropped before
// calling drain_queue below.
let mut driver = self.driver.lock().unwrap();
match Pin::new(&mut *driver).poll_next(&mut cx) {
Poll::Ready(val) => return val,
Poll::Pending => {}
};
}

// poll_next returned Pending.
// Check if any of the pending tasks tried to spawn
// some new tasks. If so, drain into the driver and loop.
if self.drain_queue() {
continue;
}

// If the driver called `wake` while we were polling,
// we should poll again immediately!
if self.is_woken.0.swap(false, Ordering::SeqCst) {
continue;
}

return None;
}
}

/// drain_queue locks both self.spawn_queue and self.driver, so it requires
/// that neither of them be locked already.
fn drain_queue(&self) -> bool {
let mut queue = self.spawn_queue.lock().unwrap();
if queue.is_empty() {
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