[PATCH bpf v4] xdp: Handle device unregister for devmap_hash map type

[Toke Høiland-Jørgensen]

It seems I forgot to add handling of devmap_hash type maps to the device
unregister hook for devmaps. This omission causes devices to not be
properly released, which causes hangs.

Fix this by adding the missing handler.

Fixes: 6f9d451ab1a3 ("xdp: Add devmap_hash map type for looking up devices by 
hashed index")
Reported-by: Tetsuo Handa <penguin-ker...@i-love.sakura.ne.jp>
Signed-off-by: Toke Høiland-Jørgensen <t...@redhat.com>
---
v4:
  - Don't forget to decrement dtab->items when removing item from map
v3:
  - Use u32 for loop iterator variable
  - Since we're holding the lock we can just iterate with 
hlist_for_each_entry_safe()
v2:
  - Grab the update lock while walking the map and removing entries.

 kernel/bpf/devmap.c | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index c0a48f336997..3867864cdc2f 100644
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c
@@ -719,6 +719,32 @@ const struct bpf_map_ops dev_map_hash_ops = {
        .map_check_btf = map_check_no_btf,
 };
 
+static void dev_map_hash_remove_netdev(struct bpf_dtab *dtab,
+                                      struct net_device *netdev)
+{
+       unsigned long flags;
+       u32 i;
+
+       spin_lock_irqsave(&dtab->index_lock, flags);
+       for (i = 0; i < dtab->n_buckets; i++) {
+               struct bpf_dtab_netdev *dev;
+               struct hlist_head *head;
+               struct hlist_node *next;
+
+               head = dev_map_index_hash(dtab, i);
+
+               hlist_for_each_entry_safe(dev, next, head, index_hlist) {
+                       if (netdev != dev->dev)
+                               continue;
+
+                       dtab->items--;
+                       hlist_del_rcu(&dev->index_hlist);
+                       call_rcu(&dev->rcu, __dev_map_entry_free);
+               }
+       }
+       spin_unlock_irqrestore(&dtab->index_lock, flags);
+}
+
 static int dev_map_notification(struct notifier_block *notifier,
                                ulong event, void *ptr)
 {
@@ -735,6 +761,11 @@ static int dev_map_notification(struct notifier_block 
*notifier,
                 */
                rcu_read_lock();
                list_for_each_entry_rcu(dtab, &dev_map_list, list) {
+                       if (dtab->map.map_type == BPF_MAP_TYPE_DEVMAP_HASH) {
+                               dev_map_hash_remove_netdev(dtab, netdev);
+                               continue;
+                       }
+
                        for (i = 0; i < dtab->map.max_entries; i++) {
                                struct bpf_dtab_netdev *dev, *odev;
 
-- 
2.23.0