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device: fix some lock ordering violations, add a test for a deadlock we hit

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Discovered by a tool + test that will come in a future change.

Updates tailscale/tailscale#19513

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
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Brad Fitzpatrick 2026-04-24 20:49:35 +00:00 • committed by 世界
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# Lock Ordering in wireguard-go/device
## Lock hierarchy
Locks must be acquired in the order listed below. A goroutine holding a
lock with a higher number must never attempt to acquire a lock with a
lower number.
```
Level 0 device.state.Mutex
Level 1 device.ipcMutex (sync.RWMutex)
Level 2 device.net.RWMutex
Level 3 device.staticIdentity.RWMutex
Level 4 device.peers.RWMutex
Level 5 peer.state.Mutex
Level 6 peer.handshake.mutex (sync.RWMutex)
Level 7 peer.keypairs.RWMutex
Level 8 device.allowedips.mu (sync.RWMutex)
Level 9 device.indexTable.RWMutex
Level 10 peer.endpoint.Mutex
Level 11 device.cookieChecker.RWMutex
Level 12 peer.cookieGenerator.RWMutex
Level 13 Timer.modifyingLock / Timer.runningLock
```
Not every pair of locks appears in practice; the ordering above is the
transitive closure of the pairs that do.