From: Martin KaFai Lau <kafai@fb.com>
Date: Wed, 4 Mar 2020 17:34:47 -0800
Subject: bpf: Return better error value in delete_elem for struct_ops map
Patch-mainline: v5.6
Git-commit: 8e5290e710f4ffe8e9f8813e2ed0397a94d7b2f1
References: bsc#1177028

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
Acked-by: Gary Lin <glin@suse.com>
---
 kernel/bpf/bpf_struct_ops.c |   14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

--- 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_ele
 	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,