Fix Issue with Concurrent Snapshot Init + Delete (#38518)

* Fix Issue with Concurrent Snapshot Init + Delete by ensuring that we're not finalizing a snapshot in the repository while it is initializing on another thread

* Closes #38489

Author: original-brownbear

server/src/main/java/org/elasticsearch/snapshots/SnapshotsService.java

@@ -331,7 +331,6 @@ public void onFailure(final Exception e) {
             public TimeValue timeout() {
                 return request.masterNodeTimeout();
             }
-
         });
     }
 
@@ -394,6 +393,8 @@ private void beginSnapshot(final ClusterState clusterState,
 
             boolean snapshotCreated;
 
+            boolean hadAbortedInitializations;
+
             @Override
             protected void doRun() {
                 assert initializingSnapshots.contains(snapshot.snapshot());
@@ -433,6 +434,8 @@ public ClusterState execute(ClusterState currentState) {
 
                             if (entry.state() == State.ABORTED) {
                                 entries.add(entry);
+                                assert entry.shards().isEmpty();
+                                hadAbortedInitializations = true;
                             } else {
                                 // Replace the snapshot that was just initialized
                                 ImmutableOpenMap<ShardId, ShardSnapshotStatus> shards =
@@ -491,6 +494,14 @@ public void clusterStateProcessed(String source, ClusterState oldState, ClusterS
                         // completion listener in this method. For the snapshot completion to work properly, the snapshot
                         // should still exist when listener is registered.
                         userCreateSnapshotListener.onResponse(snapshot.snapshot());
+
+                        if (hadAbortedInitializations) {
+                            final SnapshotsInProgress snapshotsInProgress = newState.custom(SnapshotsInProgress.TYPE);
+                            assert snapshotsInProgress != null;
+                            final SnapshotsInProgress.Entry entry = snapshotsInProgress.snapshot(snapshot.snapshot());
+                            assert entry != null;
+                            endSnapshot(entry);
+                        }
                     }
                 });
             }
@@ -701,8 +712,8 @@ public void applyClusterState(ClusterChangedEvent event) {
                     // 3. Snapshots in any other state that have all their shard tasks completed
                     snapshotsInProgress.entries().stream().filter(
                         entry -> entry.state().completed()
-                            || entry.state() == State.INIT && initializingSnapshots.contains(entry.snapshot()) == false
-                            || entry.state() != State.INIT && completed(entry.shards().values())
+                            || initializingSnapshots.contains(entry.snapshot()) == false
+                               && (entry.state() == State.INIT || completed(entry.shards().values()))
                     ).forEach(this::endSnapshot);
                 }
                 if (newMaster) {

server/src/test/java/org/elasticsearch/snapshots/DedicatedClusterSnapshotRestoreIT.java

@@ -855,7 +855,6 @@ public void testMasterShutdownDuringSnapshot() throws Exception {
         assertEquals(0, snapshotInfo.failedShards());
     }
 
-
     public void testMasterAndDataShutdownDuringSnapshot() throws Exception {
         logger.info("-->  starting three master nodes and two data nodes");
         internalCluster().startMasterOnlyNodes(3);