fix(nexus): set children to destroying state on shutdown

The existing call to destroy all nexuses on shutdown uses a reference
to the list of nexuses, which is itself mutated when a nexus is
destroyed. This can lead to a segfault on some platforms. Destroying a
nexus also leads to the child states being saved to the config file,
which is unintended.

Set all children to Destroying state instead to address both issues.

Fixes: 3ae2903 ("fix(nexus): allow re-adding child removed by AEN")

Author: jonathan-teh

mayastor/src/bdev/nexus/mod.rs

@@ -60,16 +60,14 @@ pub fn nexus_instance_new(name: String, size: u64, children: Vec<String>) {
     list.push(Nexus::new(&name, size, None, Some(&children)));
 }
 
-/// called during shutdown so that the bdevs for each child is destroyed first
-pub async fn nexus_destroy_all() {
-    info!("destroying all nexuses...");
+/// called during shutdown so that all nexus children are in Destroying state
+/// so that a possible remove event from SPDK also results in bdev removal
+pub async fn nexus_children_to_destroying_state() {
+    info!("setting all nexus children to destroying state...");
     for nexus in instances() {
-        if let Err(e) = nexus.destroy().await {
-            error!(
-                "failed to destroy nexus {} during shutdown: {}",
-                nexus.name, e
-            );
+        for child in nexus.children.iter() {
+            child.set_state(nexus_child::ChildState::Destroying);
         }
     }
-    info!("destroyed all nexuses");
+    info!("set all nexus children to destroying state");
 }

mayastor/src/core/env.rs

@@ -279,7 +279,7 @@ async fn do_shutdown(arg: *mut c_void) {
     }
 
     iscsi::fini();
-    nexus::nexus_destroy_all().await;
+    nexus::nexus_children_to_destroying_state().await;
     unsafe {
         spdk_rpc_finish();
         spdk_subsystem_fini(Some(reactors_stop), arg);