bpf: Return better error value in delete_elem for struct_ops map

The current always succeed behavior in bpf_struct_ops_map_delete_elem()
is not ideal for userspace tool.  It can be improved to return proper
error value.

If it is in TOBEFREE, it means unregistration has been already done
before but it is in progress and waiting for the subsystem to clear
the refcnt to zero, so -EINPROGRESS.

If it is INIT, it means the struct_ops has not been registered yet,
so -ENOENT.

Fixes: 85d33df357b6 ("bpf: Introduce BPF_MAP_TYPE_STRUCT_OPS")
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200305013447.535326-1-kafai@fb.com

diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index 042f95534f86db0b11148b72d64db98162dd0439..68a89a9f7ccd171dd2886ccca96a7d8fd06563a2 100644 (file)
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -482,13 +482,21 @@ static int bpf_struct_ops_map_delete_elem(struct bpf_map *map, void *key)
        prev_state = cmpxchg(&st_map->kvalue.state,
                             BPF_STRUCT_OPS_STATE_INUSE,
                             BPF_STRUCT_OPS_STATE_TOBEFREE);
-       if (prev_state == BPF_STRUCT_OPS_STATE_INUSE) {
+       switch (prev_state) {
+       case BPF_STRUCT_OPS_STATE_INUSE:
                st_map->st_ops->unreg(&st_map->kvalue.data);
                if (refcount_dec_and_test(&st_map->kvalue.refcnt))
                        bpf_map_put(map);
+               return 0;
+       case BPF_STRUCT_OPS_STATE_TOBEFREE:
+               return -EINPROGRESS;
+       case BPF_STRUCT_OPS_STATE_INIT:
+               return -ENOENT;
+       default:
+               WARN_ON_ONCE(1);
+               /* Should never happen.  Treat it as not found. */
+               return -ENOENT;
        }
-
-       return 0;
 }
 
 static void bpf_struct_ops_map_seq_show_elem(struct bpf_map *map, void *key,