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orchestrator: NBDProvider.Close() syncs device before disconnecting, causing spurious EIO on sandbox cleanup after VM crash

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2/5
预计耗时
1-3 小时
新手友好度
75/100
Issue 类型
缺陷
描述清晰度
描述清楚
活跃度
冷清
技术栈
go
领域
infrastructure

调研方向

从 packages/orchestrator/pkg/sandbox/rootfs/nbd.go 开始，重点关注 NBDProvider.Close() 和 sync()。验证 VM 崩溃后的清理行为：sync() 返回的 EIO 应记录为 WARN，但不应作为清理错误向上传播，而其他 sync 错误仍应继续传播。

由索引模型根据 Issue 内容生成。

描述

Describe the bug

When a Firecracker VM exits abnormally (OOM-kill, crash, etc.), NBDProvider.Close() in packages/orchestrator/pkg/sandbox/rootfs/nbd.go calls sync() before mnt.Close(). Because the NBD device is already in an error state after the VM dies, the ioctl(BLKFLSBUF) + fsync inside sync() returns EIO. This causes every sandbox cleanup after an abnormal VM exit to log:

failed to cleanup sandbox: error flushing cow device: failed to fsync path: input/output error

even though no data loss has occurred — the error is an expected consequence of the VM being dead, not a real storage failure.

Root cause

NBDProvider.Close() (line 130 of rootfs/nbd.go):

func (o *NBDProvider) Close(ctx context.Context) error {
    var errs []error

    err := o.sync(ctx)         // ← calls BLKFLSBUF ioctl + fsync on /dev/nbdX
    if err != nil {
        errs = append(errs, fmt.Errorf("error flushing cow device: %w", err))
    }

    err = o.mnt.Close(ctx)     // ← disconnects the NBD device (too late)
    ...
}

sync() (line 162) opens /dev/nbdX, issues BLKFLSBUF, then calls flush() which does syscall.Fsync. When the VM has already crashed, the NBD device is in error state and Fsync returns syscall.EIO. The error propagates up through Sandbox.Close() → setupSandboxLifecycle() which logs it at ERROR level.

Expected behavior

EIO from sync() during sandbox cleanup should be treated as an expected condition (VM died, no data to flush) and logged at WARN level rather than propagating as an error that triggers the "failed to cleanup sandbox" ERROR log.

Impact

  • Spurious "failed to cleanup sandbox" ERROR log on every abnormal VM exit
  • Noise in production alerting / on-call signals

Suggested fix

In NBDProvider.Close(), detect syscall.EIO from sync() and downgrade to a warning:

err := o.sync(ctx)
if err != nil {
    if errors.Is(err, syscall.EIO) {
        logger.L().Warn(ctx, "error flushing cow device (VM likely crashed, ignoring)", zap.Error(err))
    } else {
        errs = append(errs, fmt.Errorf("error flushing cow device: %w", err))
    }
}

Environment

  • Bare-metal deployment with Nomad
  • Observed under high sandbox creation load (thundering herd from client retries)
主要语言
Go
星标
1.6k
派生
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