If a packet arrives while WireGuard is being reconfigured with b.mu held, such as during a profile switch,
calling back into (*LocalBackend).GetPeerAPIPort from (*Wrapper).filterPacketInboundFromWireGuard
may deadlock when it tries to acquire b.mu.
This occurs because a peer cannot be removed while an inbound packet is being processed.
The reconfig and profile switch wait for (*Peer).RoutineSequentialReceiver to return, but it never finishes
because GetPeerAPIPort needs b.mu, which the waiting goroutine already holds.
In this PR, we make peerAPIPorts a new syncs.AtomicValue field that is written with b.mu held
but can be read by GetPeerAPIPort without holding the mutex, which fixes the deadlock.
There might be other long-term ways to address the issue, such as moving peer API listeners
from LocalBackend to nodeBackend so they can be accessed without holding b.mu,
but these changes are too large and risky at this stage in the v1.92 release cycle.
Updates #18124
Signed-off-by: Nick Khyl <nickk@tailscale.com>
(cherry picked from commit 557457f3c2)
fd7dd6433f