[PATCH bpf-next v4 2/2] xsk: support BPF_EXIST and BPF_NOEXIST flags in XSKMAP

[Björn Töpel]

From: Björn Töpel <bjorn.to...@intel.com>

The XSKMAP did not honor the BPF_EXIST/BPF_NOEXIST flags when updating
an entry. This patch addresses that.

Signed-off-by: Björn Töpel <bjorn.to...@intel.com>
---
 kernel/bpf/xskmap.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/kernel/bpf/xskmap.c b/kernel/bpf/xskmap.c
index 780639309f6b..8864dfe1d9ef 100644
--- a/kernel/bpf/xskmap.c
+++ b/kernel/bpf/xskmap.c
@@ -226,8 +226,6 @@ static int xsk_map_update_elem(struct bpf_map *map, void 
*key, void *value,
                return -EINVAL;
        if (unlikely(i >= m->map.max_entries))
                return -E2BIG;
-       if (unlikely(map_flags == BPF_NOEXIST))
-               return -EEXIST;
 
        sock = sockfd_lookup(fd, &err);
        if (!sock)
@@ -253,14 +251,29 @@ static int xsk_map_update_elem(struct bpf_map *map, void 
*key, void *value,
        }
 
        spin_lock_bh(&m->lock);
+       entry = &m->xsk_map[i];
+       old_xs = READ_ONCE(*entry);
+       if (old_xs && map_flags == BPF_NOEXIST) {
+               err = -EEXIST;
+               goto out;
+       } else if (!old_xs && map_flags == BPF_EXIST) {
+               err = -ENOENT;
+               goto out;
+       }
        xsk_map_sock_add(xs, node);
-       old_xs = xchg(entry, xs);
+       WRITE_ONCE(*entry, xs);
        if (old_xs)
                xsk_map_sock_delete(old_xs, entry);
        spin_unlock_bh(&m->lock);
 
        sockfd_put(sock);
        return 0;
+
+out:
+       spin_unlock_bh(&m->lock);
+       sockfd_put(sock);
+       xsk_map_node_free(node);
+       return err;
 }
 
 static int xsk_map_delete_elem(struct bpf_map *map, void *key)
-- 
2.20.1