Open-Mesh » batman-adv

https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260831135117.574836-1-sw%40simonwunderlich.de?part=12

Can deferring batadv_tt_global_del_orig_list() until after flags_lock is
dropped lose an originator entry added in between?

The old code purged the originator list first and cleared
BATADV_TT_CLIENT_TEMP / BATADV_TT_CLIENT_ROAM afterwards, so a second
context still saw the flag and did its own purge. Now the cleared flag is
published before the list is wiped:

 
 CPU0 batadv_tt_global_add()             CPU1 batadv_tt_global_add()
   spin_lock_bh(&common->flags_lock);
   delete = true;
   common->flags &= ~BATADV_TT_CLIENT_TEMP;
   spin_unlock_bh(&common->flags_lock);
                                         spin_lock_bh(&common->flags_lock);
                                         /* TEMP already clear, so
                                          * delete stays false
                                          */
                                         spin_unlock_bh(&common->flags_lock);
                                         batadv_tt_global_orig_entry_add()
   batadv_tt_global_del_orig_list()
     /* drops every orig entry,
      * including CPU1's fresh one
      */

batadv_tt_global_del_orig_list() takes tt_global_entry->list_lock and
removes all entries:

     spin_lock_bh(&tt_global_entry->list_lock);
     head = &tt_global_entry->orig_list;
     hlist_for_each_entry_safe(orig_entry, safe, head, list)
         _batadv_tt_global_del_orig_entry(tt_global_entry, orig_entry);

Both callers return true in that case, so does the route via CPU1's
originator silently disappear until the next global CRC mismatch triggers
a fresh TT request? batadv_tt_global_add() is reached from received TT
TVLV data (serialized only per originator by orig_node->tt_lock) and from
batadv_tt_add_temporary_global_entry(), so two CPUs can process
announcements for the same client from different originators at the same
time.