Use atomic.Value for Stack.tcpProbeFunc.

b/166980357#comment56 shows:

- 837 goroutines blocked in:
gvisor/pkg/sync/sync.(*RWMutex).Lock
gvisor/pkg/tcpip/stack/stack.(*Stack).StartTransportEndpointCleanup
gvisor/pkg/tcpip/transport/tcp/tcp.(*endpoint).cleanupLocked
gvisor/pkg/tcpip/transport/tcp/tcp.(*endpoint).completeWorkerLocked
gvisor/pkg/tcpip/transport/tcp/tcp.(*endpoint).protocolMainLoop.func1
gvisor/pkg/tcpip/transport/tcp/tcp.(*endpoint).protocolMainLoop

- 695 goroutines blocked in:
gvisor/pkg/sync/sync.(*RWMutex).Lock
gvisor/pkg/tcpip/stack/stack.(*Stack).CompleteTransportEndpointCleanup
gvisor/pkg/tcpip/transport/tcp/tcp.(*endpoint).cleanupLocked
gvisor/pkg/tcpip/transport/tcp/tcp.(*endpoint).completeWorkerLocked
gvisor/pkg/tcpip/transport/tcp/tcp.(*endpoint).protocolMainLoop.func1
gvisor/pkg/tcpip/transport/tcp/tcp.(*endpoint).protocolMainLoop

- 3882 goroutines blocked in:
gvisor/pkg/sync/sync.(*RWMutex).Lock
gvisor/pkg/tcpip/stack/stack.(*Stack).GetTCPProbe
gvisor/pkg/tcpip/transport/tcp/tcp.newEndpoint
gvisor/pkg/tcpip/transport/tcp/tcp.(*protocol).NewEndpoint
gvisor/pkg/tcpip/stack/stack.(*Stack).NewEndpoint

All of these are contending on Stack.mu. Stack.StartTransportEndpointCleanup()
and Stack.CompleteTransportEndpointCleanup() insert/delete TransportEndpoints
in a map (Stack.cleanupEndpoints), and the former also does endpoint
unregistration while holding Stack.mu, so it's not immediately clear how
feasible it is to replace the map with a mutex-less implementation or how much
doing so would help. However, Stack.GetTCPProbe() just reads a function object
(Stack.tcpProbeFunc) that is almost always nil (as far as I can tell,
Stack.AddTCPProbe() is only called in tests), and it's called for every new TCP
endpoint. So converting it to an atomic.Value should significantly reduce
contention on Stack.mu, improving TCP endpoint creation latency and allowing
TCP endpoint cleanup to proceed.

PiperOrigin-RevId: 330004140

0 files changed, 0 insertions, 0 deletions