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embassy-net: Avoid looping if the link is down #5860

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bugadani wants to merge 1 commit into from
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embassy-net: Avoid looping if the link is down #5860

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2 changes: 2 additions & 0 deletions embassy-net/CHANGELOG.md
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Expand Up @@ -8,6 +8,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
<!-- next-header -->
## Unreleased - ReleaseDate

- Avoid looping forever if the network interface is down.

## 0.9.0 - 2026-03-10

- raw: Removed unnecessary Driver type parameter from `RawSocket::new`
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10 changes: 6 additions & 4 deletions embassy-net/src/lib.rs
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Expand Up @@ -961,10 +961,12 @@ impl Inner {
self.apply_static_config()
}

if let Some(poll_at) = self.iface.poll_at(timestamp, &mut self.sockets) {
let t = pin!(Timer::at(instant_from_smoltcp(poll_at)));
if t.poll(cx).is_ready() {
cx.waker().wake_by_ref();
if self.link_up {
if let Some(poll_at) = self.iface.poll_at(timestamp, &mut self.sockets) {
let t = pin!(Timer::at(instant_from_smoltcp(poll_at)));
if t.poll(cx).is_ready() {
cx.waker().wake_by_ref();
}
}
}
Comment on lines +964 to 971
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Copilot AI Apr 16, 2026

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Gating iface.poll_at(...) on self.link_up prevents the runner from scheduling any future polls while the link is down. That can stop smoltcp’s time-based state machine from progressing (e.g., TCP set_timeout() / keep-alive timers) and may cause socket operations to hang indefinitely during a prolonged link-down period, despite the docs stating timeouts close the socket after the specified duration.

Consider still calling poll_at when the link is down, but suppress only the immediate re-poll case that causes the busy loop (e.g., if poll_at <= timestamp and !link_up, don’t wake immediately; optionally apply a small backoff), while still scheduling when poll_at is in the future so protocol/socket timers continue to run.

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}
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