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io: fix race in Mock::poll_write (#7882)

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ADD-SP
2026-02-23 20:49:37 -08:00
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parent f21f2693f0
commit d18e5dfbb0
1 changed files with 24 additions and 1 deletions
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tokio-test/src/io.rs
+24 -1
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@@ -438,7 +438,30 @@ impl AsyncWrite for Mock {
let until = Instant::now() + rem; let until = Instant::now() + rem;
self.inner.sleep = Some(Box::pin(time::sleep_until(until))); self.inner.sleep = Some(Box::pin(time::sleep_until(until)));
} else { } else {
panic!("unexpected WouldBlock {}", self.pmsg()); // A race condition (TOCTOU) can occur if the
// timer expires between the `write()` call
// and `remaining_wait()` due to preemption or other
// delays. In this case, the `Wait` action is already popped by
// `action()`, so we continue to the next one.
//
// Consider the following sequence:
//
// poll_write Inner action()
// |--write()--->| |
// | |--action()---->| (returns Wait)
// |<-WouldBlk---| |
// | | |
// | <--- TIMEOUT! ---> |
// | (due to preemption, etc.) |
// | | |
// |-rem_wait()->| |
// | |--action()---->| (time's up, pop Wait)
// |<--None------| |
// | | |
// |---continue->| (process next action)
//
// See <https://github.com/tokio-rs/tokio/issues/7881>.
continue;
} }
} }
Ok(0) => { Ok(0) => {