firecracker-microvm/firecracker · error

poisoned lock

Error message

poisoned lock

What it means

Error "poisoned lock" thrown in firecracker-microvm/firecracker.

Source

Thrown at src/vmm/src/logger/metrics.rs:153

    /// Upon success, the function will return `True` (if metrics system was initialized and metrics
    /// were successfully written to disk) or `False` (if metrics system was not yet initialized).
    ///
    /// This function is usually supposed to be called only from a single thread and
    /// is not meant to be used in a multithreaded scenario. The reason
    /// `metrics_buf` is enclosed in a `Mutex` is that `lazy_static` enforces
    /// thread-safety on all its members.
    /// The only exception is for signal handlers that result in process exit, which may be run on
    /// any thread. To prevent the race condition present in the serialisation step of
    /// SharedIncMetrics, deadly signals use SharedStoreMetrics instead (which have a thread-safe
    /// serialise implementation).
    /// The only known caveat is that other metrics may not be properly written before exiting from
    /// a signal handler. We make this compromise since the process will be killed anyway and the
    /// important metric in this case is the signal one.
    /// The alternative is to hold a Mutex over the entire function call, but this increases the
    /// known deadlock potential.
    pub fn write(&self) -> Result<bool, MetricsError> {
        if let Some(lock) = self.metrics_buf.get() {
            let mut writer = lock.lock().expect("poisoned lock");
            serde_json::to_writer(writer.by_ref(), &self.app_metrics)
                .map_err(|err| MetricsError::Serde(err.to_string()))?;
            writer.write_all(b"\n").map_err(MetricsError::Write)?;
            Ok(true)
        } else {
            // If the metrics are not initialized, no error is thrown but we do let the user know
            // that metrics were not written.
            Ok(false)
        }
    }
}

impl<T: Serialize + Debug, M: Write + Send + Debug> Deref for Metrics<T, M> {
    type Target = T;

    fn deref(&self) -> &Self::Target {
        &self.app_metrics
    }

View on GitHub (pinned to 0a745def42)

Solutions

1. Find and fix the earlier panic that poisoned the metrics lock.
2. Recover with into_inner() only if the metrics state is provably consistent after the panic.

When it happens

Trigger: Thrown at src/vmm/src/logger/metrics.rs:153 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of firecracker-microvm/firecracker@0a745def42 (2026-08-19). Data as JSON: /api/errors/fdcdc85522bb9d31. Report an issue: GitHub.