Tweak head syncing (#1845)

## Issue Addressed

Fixes head syncing

## Proposed Changes

- Get back to statusing peers after removing chain segments and making the peer manager deal with status according to the Sync status, preventing an old known deadlock
- Also a bug where a chain would get removed if the optimistic batch succeeds being empty

## Additional Info

Tested on Medalla and looking good

beacon_node/eth2_libp2p/src/peer_manager/mod.rs

@@ -3,6 +3,7 @@
 pub use self::peerdb::*;
 use crate::discovery::{subnet_predicate, Discovery, DiscoveryEvent, TARGET_SUBNET_PEERS};
 use crate::rpc::{GoodbyeReason, MetaData, Protocol, RPCError, RPCResponseErrorCode};
+use crate::types::SyncState;
 use crate::{error, metrics};
 use crate::{EnrExt, NetworkConfig, NetworkGlobals, PeerId, SubnetDiscovery};
 use futures::prelude::*;
@@ -844,16 +845,19 @@ impl<TSpec: EthSpec> Stream for PeerManager<TSpec> {
             }
         }
 
-        loop {
-            match self.status_peers.poll_next_unpin(cx) {
-                Poll::Ready(Some(Ok(peer_id))) => {
-                    self.status_peers.insert(peer_id.clone());
-                    self.events.push(PeerManagerEvent::Status(peer_id))
+        if !matches!(self.network_globals.sync_state(), SyncState::SyncingFinalized{..}|SyncState::SyncingHead{..})
+        {
+            loop {
+                match self.status_peers.poll_next_unpin(cx) {
+                    Poll::Ready(Some(Ok(peer_id))) => {
+                        self.status_peers.insert(peer_id.clone());
+                        self.events.push(PeerManagerEvent::Status(peer_id))
+                    }
+                    Poll::Ready(Some(Err(e))) => {
+                        error!(self.log, "Failed to check for peers to ping"; "error" => e.to_string())
+                    }
+                    Poll::Ready(None) | Poll::Pending => break,
                 }
-                Poll::Ready(Some(Err(e))) => {
-                    error!(self.log, "Failed to check for peers to ping"; "error" => e.to_string())
-                }
-                Poll::Ready(None) | Poll::Pending => break,
             }
         }
 

beacon_node/eth2_libp2p/src/types/sync_state.rs

@@ -10,6 +10,9 @@ pub enum SyncState {
     /// The node is performing a long-range (batch) sync over one or many head chains.
     /// In this state parent lookups are disabled.
     SyncingHead { start_slot: Slot, target_slot: Slot },
+    /// The node has identified the need for is sync operations and is transitioning to a syncing
+    /// state.
+    SyncTransition,
     /// The node is up to date with all known peers and is connected to at least one
     /// fully synced peer. In this state, parent lookups are enabled.
     Synced,
@@ -25,6 +28,7 @@ impl PartialEq for SyncState {
             (SyncState::SyncingHead { .. }, SyncState::SyncingHead { .. }) => true,
             (SyncState::Synced, SyncState::Synced) => true,
             (SyncState::Stalled, SyncState::Stalled) => true,
+            (SyncState::SyncTransition, SyncState::SyncTransition) => true,
             _ => false,
         }
     }
@@ -36,6 +40,7 @@ impl SyncState {
         match self {
             SyncState::SyncingFinalized { .. } => true,
             SyncState::SyncingHead { .. } => true,
+            SyncState::SyncTransition => true,
             SyncState::Synced => false,
             SyncState::Stalled => false,
         }
@@ -54,6 +59,7 @@ impl std::fmt::Display for SyncState {
             SyncState::SyncingHead { .. } => write!(f, "Syncing Head Chain"),
             SyncState::Synced { .. } => write!(f, "Synced"),
             SyncState::Stalled { .. } => write!(f, "Stalled"),
+            SyncState::SyncTransition => write!(f, "Searching syncing peers"),
         }
     }
 }