Merge #123151

123151: kvclient: check for invalid routing token r=arulajmani a=andrewbaptist

Previously in `DistSender.sendPartialBatch` we could hit an error path during processing of a proxy request if the method was called with an invalid token. This could happen if there was a range split or merge which could invalidate the routing token prior to the method being called.

This fix validates the token is not null before attempting to Sync.

Epic: none
Fixes: #123146

Release note: None

Co-authored-by: Andrew Baptist <baptist@cockroachlabs.com>

pkg/kv/kvclient/kvcoord/dist_sender.go

@@ -2047,7 +2047,17 @@ func (ds *DistSender) sendPartialBatch(
 		// and our local replica before attempting the request. If the sync
 		// makes our token invalid, we handle it similarly to a RangeNotFound or
 		// NotLeaseHolderError from a remote server.
-		if ba.ProxyRangeInfo != nil {
+		// NB: The routingTok is usually valid when we get to this line on a
+		// proxy request since we never retry the outer for loop, however there
+		// is an edge case where we invalidate the token once here and then
+		// invalidate it a second time in the statement below and hit a
+		// retriable range loopup error.
+		// TODO(baptist): Consider splitting out the handling in this method for
+		// proxy requests vs non-proxy requests. Currently it is hard to follow
+		// the invariants when this is called. Alternativly move this call to be
+		// done immediately when the routingTok is created as it will always be
+		// valid at that point.
+		if ba.ProxyRangeInfo != nil && routingTok.Valid() {
 			routingTok.SyncTokenAndMaybeUpdateCache(ctx, &ba.ProxyRangeInfo.Lease, &ba.ProxyRangeInfo.Desc)
 		}
 		if !routingTok.Valid() {