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virtio_net: handle unexpected tx completion without panicking #2778

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virtio_net: handle unexpected tx completion without panicking #2778

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virtio_net: handle unexpected tx completion without panicking
Feb 10, 2026
2de5dee
Merge branch 'main' into fix/virtio_net-tx-completion-panic
benhillis Apr 8, 2026
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24 changes: 23 additions & 1 deletion vm/devices/virtio/virtio_net/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1305,7 +1305,29 @@ impl Worker {

fn complete_tx_packet(&mut self, id: TxId) -> Result<(), WorkerError> {
let state = &mut self.active_state;
let tx_packet = state.pending_tx_packets[id.0 as usize].take().unwrap();
let idx = id.0 as usize;
let pending_len = state.pending_tx_packets.len();
Comment on lines +1308 to +1309
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Copilot AI Apr 8, 2026

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id.0 as usize can silently truncate if id.0 is wider than usize (or if this ever builds/runs in a 32-bit environment). Since this function is explicitly handling unexpected IDs, it would be safer to use a checked conversion (e.g., usize::try_from(id.0)) and treat conversion failure the same as out-of-range.

Suggested change
let idx = id.0 as usize;
let pending_len = state.pending_tx_packets.len();
let pending_len = state.pending_tx_packets.len();
let Ok(idx) = usize::try_from(id.0) else {
tracelimit::error_ratelimited!(
tx_id = id.0,
pending_tx_packets_len = pending_len,
"unexpected tx completion for out-of-range packet"
);
return Ok(());
};

Copilot uses AI. Check for mistakes.

let Some(slot) = state.pending_tx_packets.get_mut(idx) else {
tracelimit::error_ratelimited!(
tx_id = id.0,
tx_index = idx,
pending_tx_packets_len = pending_len,
"unexpected tx completion for out-of-range packet"
);
return Ok(());
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Copilot AI Apr 8, 2026

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For an out-of-range TxId, returning Ok(()) may allow the device to continue operating in a potentially corrupted backend/driver state. Consider returning a WorkerError (or otherwise triggering a reset/reconnect path) for the out-of-range case while still tolerating duplicate completions (slot.take() == None) if those can happen benignly.

Suggested change
return Ok(());
return Err(anyhow::anyhow!(
"unexpected tx completion for out-of-range packet: tx_id={}, tx_index={}, pending_tx_packets_len={}",
id.0,
idx,
pending_len
)
.into());

Copilot uses AI. Check for mistakes.
};

let Some(tx_packet) = slot.take() else {
tracelimit::error_ratelimited!(
tx_id = id.0,
tx_index = idx,
pending_tx_packets_len = pending_len,
"unexpected tx completion for already-completed packet"
);
return Ok(());
};

self.virtio_state.tx_queue.complete(tx_packet.work, 0);
self.active_state.stats.tx_packets.increment();
Ok(())
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