Potential race condition in p2p.switch.reconnectToPeer() and pex_reactor

[lklimek]

Tendermint version master (revision 6be3661)

What happened:

When reviewing the code, I have noticed two potential race condition bugs:

• Reactor.RequestAddrs()
• Switch.reconnectToPeer()

Here's the faulty code:

1. if r.requestsSent.Has(id) {
2.   return
3. }
4. r.requestsSent.Set(id, struct{}{})

If two goroutines enter these functions at the same time, they both can pass the Has() condition in line 1 (as it's not set yet), and then, both execute the Set() operation from line 4 in random order, resulting in a non-deterministic behavior.

A possible solution is to use an approach similar to sync.Map.LoadOrStore() to do operations from lines 1 and 4 together, in an atomic way.