devlink: Count struct devlink consumers

The struct devlink itself is protected by internal lock and doesn't
need global lock during operation. That global lock is used to protect
addition/removal new devlink instances from the global list in use by
all devlink consumers in the system.

The future conversion of linked list to be xarray will allow us to
actually delete that lock, but first we need to count all struct devlink
users.

The reference counting provides us a way to ensure that no new user
space commands success to grab devlink instance which is going to be
destroyed makes it is safe to access it without lock.

Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 172 insertions, 35 deletions

diff --git a/include/net/devlink.h b/include/net/devlink.h
index 1151497c0ec5..4c60d61d92da 100644
--- a/include/net/devlink.h
+++ b/include/net/devlink.h
@@ -56,6 +56,8 @@ struct devlink {
 			    */
 	u8 reload_failed:1,
 	   reload_enabled:1;
+	refcount_t refcount;
+	struct completion comp;
 	char priv[0] __aligned(NETDEV_ALIGN);
 };
 
diff --git a/net/core/devlink.c b/net/core/devlink.c
index c8a8eecad1c5..76f459da6e05 100644
--- a/net/core/devlink.c
+++ b/net/core/devlink.c
@@ -108,10 +108,22 @@ struct net *devlink_net(const struct devlink *devlink)
 }
 EXPORT_SYMBOL_GPL(devlink_net);
 
+static void devlink_put(struct devlink *devlink)
+{
+	if (refcount_dec_and_test(&devlink->refcount))
+		complete(&devlink->comp);
+}
+
+static bool __must_check devlink_try_get(struct devlink *devlink)
+{
+	return refcount_inc_not_zero(&devlink->refcount);
+}
+
 static struct devlink *devlink_get_from_attrs(struct net *net,
 					      struct nlattr **attrs)
 {
 	struct devlink *devlink;
+	bool found = false;
 	char *busname;
 	char *devname;
 
@@ -126,16 +138,16 @@ static struct devlink *devlink_get_from_attrs(struct net *net,
 	list_for_each_entry(devlink, &devlink_list, list) {
 		if (strcmp(devlink->dev->bus->name, busname) == 0 &&
 		    strcmp(dev_name(devlink->dev), devname) == 0 &&
-		    net_eq(devlink_net(devlink), net))
-			return devlink;
+		    net_eq(devlink_net(devlink), net)) {
+			found = true;
+			break;
+		}
 	}
 
-	return ERR_PTR(-ENODEV);
-}
+	if (!found || !devlink_try_get(devlink))
+		devlink = ERR_PTR(-ENODEV);
 
-static struct devlink *devlink_get_from_info(struct genl_info *info)
-{
-	return devlink_get_from_attrs(genl_info_net(info), info->attrs);
+	return devlink;
 }
 
 static struct devlink_port *devlink_port_get_by_index(struct devlink *devlink,
@@ -486,7 +498,7 @@ static int devlink_nl_pre_doit(const struct genl_ops *ops,
 	int err;
 
 	mutex_lock(&devlink_mutex);
-	devlink = devlink_get_from_info(info);
+	devlink = devlink_get_from_attrs(genl_info_net(info), info->attrs);
 	if (IS_ERR(devlink)) {
 		mutex_unlock(&devlink_mutex);
 		return PTR_ERR(devlink);
@@ -529,6 +541,7 @@ static int devlink_nl_pre_doit(const struct genl_ops *ops,
 unlock:
 	if (~ops->internal_flags & DEVLINK_NL_FLAG_NO_LOCK)
 		mutex_unlock(&devlink->lock);
+	devlink_put(devlink);
 	mutex_unlock(&devlink_mutex);
 	return err;
 }
@@ -541,6 +554,7 @@ static void devlink_nl_post_doit(const struct genl_ops *ops,
 	devlink = info->user_ptr[0];
 	if (~ops->internal_flags & DEVLINK_NL_FLAG_NO_LOCK)
 		mutex_unlock(&devlink->lock);
+	devlink_put(devlink);
 	mutex_unlock(&devlink_mutex);
 }
 
@@ -1078,8 +1092,12 @@ static int devlink_nl_cmd_rate_get_dumpit(struct sk_buff *msg,
 
 	mutex_lock(&devlink_mutex);
 	list_for_each_entry(devlink, &devlink_list, list) {
-		if (!net_eq(devlink_net(devlink), sock_net(msg->sk)))
+		if (!devlink_try_get(devlink))
 			continue;
+
+		if (!net_eq(devlink_net(devlink), sock_net(msg->sk)))
+			goto retry;
+
 		mutex_lock(&devlink->lock);
 		list_for_each_entry(devlink_rate, &devlink->rate_list, list) {
 			enum devlink_command cmd = DEVLINK_CMD_RATE_NEW;
@@ -1094,11 +1112,14 @@ static int devlink_nl_cmd_rate_get_dumpit(struct sk_buff *msg,
 						   NLM_F_MULTI, NULL);
 			if (err) {
 				mutex_unlock(&devlink->lock);
+				devlink_put(devlink);
 				goto out;
 			}
 			idx++;
 		}
 		mutex_unlock(&devlink->lock);
+retry:
+		devlink_put(devlink);
 	}
 out:
 	mutex_unlock(&devlink_mutex);
@@ -1173,15 +1194,24 @@ static int devlink_nl_cmd_get_dumpit(struct sk_buff *msg,
 
 	mutex_lock(&devlink_mutex);
 	list_for_each_entry(devlink, &devlink_list, list) {
-		if (!net_eq(devlink_net(devlink), sock_net(msg->sk)))
+		if (!devlink_try_get(devlink))
 			continue;
+
+		if (!net_eq(devlink_net(devlink), sock_net(msg->sk))) {
+			devlink_put(devlink);
+			continue;
+		}
+
 		if (idx < start) {
 			idx++;
+			devlink_put(devlink);
 			continue;
 		}
+
 		err = devlink_nl_fill(msg, devlink, DEVLINK_CMD_NEW,
 				      NETLINK_CB(cb->skb).portid,
 				      cb->nlh->nlmsg_seq, NLM_F_MULTI);
+		devlink_put(devlink);
 		if (err)
 			goto out;
 		idx++;
@@ -1226,8 +1256,12 @@ static int devlink_nl_cmd_port_get_dumpit(struct sk_buff *msg,
 
 	mutex_lock(&devlink_mutex);
 	list_for_each_entry(devlink, &devlink_list, list) {
-		if (!net_eq(devlink_net(devlink), sock_net(msg->sk)))
+		if (!devlink_try_get(devlink))
 			continue;
+
+		if (!net_eq(devlink_net(devlink), sock_net(msg->sk)))
+			goto retry;
+
 		mutex_lock(&devlink->lock);
 		list_for_each_entry(devlink_port, &devlink->port_list, list) {
 			if (idx < start) {
@@ -1241,11 +1275,14 @@ static int devlink_nl_cmd_port_get_dumpit(struct sk_buff *msg,
 						   NLM_F_MULTI, cb->extack);
 			if (err) {
 				mutex_unlock(&devlink->lock);
+				devlink_put(devlink);
 				goto out;
 			}
 			idx++;
 		}
 		mutex_unlock(&devlink->lock);
+retry:
+		devlink_put(devlink);
 	}
 out:
 	mutex_unlock(&devlink_mutex);
@@ -1884,8 +1921,12 @@ static int devlink_nl_cmd_sb_get_dumpit(struct sk_buff *msg,
 
 	mutex_lock(&devlink_mutex);
 	list_for_each_entry(devlink, &devlink_list, list) {
-		if (!net_eq(devlink_net(devlink), sock_net(msg->sk)))
+		if (!devlink_try_get(devlink))
 			continue;
+
+		if (!net_eq(devlink_net(devlink), sock_net(msg->sk)))
+			goto retry;
+
 		mutex_lock(&devlink->lock);
 		list_for_each_entry(devlink_sb, &devlink->sb_list, list) {
 			if (idx < start) {
@@ -1899,11 +1940,14 @@ static int devlink_nl_cmd_sb_get_dumpit(struct sk_buff *msg,
 						 NLM_F_MULTI);
 			if (err) {
 				mutex_unlock(&devlink->lock);
+				devlink_put(devlink);
 				goto out;
 			}
 			idx++;
 		}
 		mutex_unlock(&devlink->lock);
+retry:
+		devlink_put(devlink);
 	}
 out:
 	mutex_unlock(&devlink_mutex);
@@ -2028,9 +2072,13 @@ static int devlink_nl_cmd_sb_pool_get_dumpit(struct sk_buff *msg,
 
 	mutex_lock(&devlink_mutex);
 	list_for_each_entry(devlink, &devlink_list, list) {
+		if (!devlink_try_get(devlink))
+			continue;
+
 		if (!net_eq(devlink_net(devlink), sock_net(msg->sk)) ||
 		    !devlink->ops->sb_pool_get)
-			continue;
+			goto retry;
+
 		mutex_lock(&devlink->lock);
 		list_for_each_entry(devlink_sb, &devlink->sb_list, list) {
 			err = __sb_pool_get_dumpit(msg, start, &idx, devlink,
@@ -2041,10 +2089,13 @@ static int devlink_nl_cmd_sb_pool_get_dumpit(struct sk_buff *msg,
 				err = 0;
 			} else if (err) {
 				mutex_unlock(&devlink->lock);
+				devlink_put(devlink);
 				goto out;
 			}
 		}
 		mutex_unlock(&devlink->lock);
+retry:
+		devlink_put(devlink);
 	}
 out:
 	mutex_unlock(&devlink_mutex);
@@ -2241,9 +2292,13 @@ static int devlink_nl_cmd_sb_port_pool_get_dumpit(struct sk_buff *msg,
 
 	mutex_lock(&devlink_mutex);
 	list_for_each_entry(devlink, &devlink_list, list) {
+		if (!devlink_try_get(devlink))
+			continue;
+
 		if (!net_eq(devlink_net(devlink), sock_net(msg->sk)) ||
 		    !devlink->ops->sb_port_pool_get)
-			continue;
+			goto retry;
+
 		mutex_lock(&devlink->lock);
 		list_for_each_entry(devlink_sb, &devlink->sb_list, list) {
 			err = __sb_port_pool_get_dumpit(msg, start, &idx,
@@ -2254,10 +2309,13 @@ static int devlink_nl_cmd_sb_port_pool_get_dumpit(struct sk_buff *msg,
 				err = 0;
 			} else if (err) {
 				mutex_unlock(&devlink->lock);
+				devlink_put(devlink);
 				goto out;
 			}
 		}
 		mutex_unlock(&devlink->lock);
+retry:
+		devlink_put(devlink);
 	}
 out:
 	mutex_unlock(&devlink_mutex);
@@ -2482,9 +2540,12 @@ devlink_nl_cmd_sb_tc_pool_bind_get_dumpit(struct sk_buff *msg,
 
 	mutex_lock(&devlink_mutex);
 	list_for_each_entry(devlink, &devlink_list, list) {
+		if (!devlink_try_get(devlink))
+			continue;
+
 		if (!net_eq(devlink_net(devlink), sock_net(msg->sk)) ||
 		    !devlink->ops->sb_tc_pool_bind_get)
-			continue;
+			goto retry;
 
 		mutex_lock(&devlink->lock);
 		list_for_each_entry(devlink_sb, &devlink->sb_list, list) {
@@ -2497,10 +2558,13 @@ devlink_nl_cmd_sb_tc_pool_bind_get_dumpit(struct sk_buff *msg,
 				err = 0;
 			} else if (err) {
 				mutex_unlock(&devlink->lock);
+				devlink_put(devlink);
 				goto out;
 			}
 		}
 		mutex_unlock(&devlink->lock);
+retry:
+		devlink_put(devlink);
 	}
 out:
 	mutex_unlock(&devlink_mutex);
@@ -4552,8 +4616,12 @@ static int devlink_nl_cmd_param_get_dumpit(struct sk_buff *msg,
 
 	mutex_lock(&devlink_mutex);
 	list_for_each_entry(devlink, &devlink_list, list) {
-		if (!net_eq(devlink_net(devlink), sock_net(msg->sk)))
+		if (!devlink_try_get(devlink))
 			continue;
+
+		if (!net_eq(devlink_net(devlink), sock_net(msg->sk)))
+			goto retry;
+
 		mutex_lock(&devlink->lock);
 		list_for_each_entry(param_item, &devlink->param_list, list) {
 			if (idx < start) {
@@ -4569,11 +4637,14 @@ static int devlink_nl_cmd_param_get_dumpit(struct sk_buff *msg,
 				err = 0;
 			} else if (err) {
 				mutex_unlock(&devlink->lock);
+				devlink_put(devlink);
 				goto out;
 			}
 			idx++;
 		}
 		mutex_unlock(&devlink->lock);
+retry:
+		devlink_put(devlink);
 	}
 out:
 	mutex_unlock(&devlink_mutex);
@@ -4820,8 +4891,12 @@ static int devlink_nl_cmd_port_param_get_dumpit(struct sk_buff *msg,
 
 	mutex_lock(&devlink_mutex);
 	list_for_each_entry(devlink, &devlink_list, list) {
-		if (!net_eq(devlink_net(devlink), sock_net(msg->sk)))
+		if (!devlink_try_get(devlink))
 			continue;
+
+		if (!net_eq(devlink_net(devlink), sock_net(msg->sk)))
+			goto retry;
+
 		mutex_lock(&devlink->lock);
 		list_for_each_entry(devlink_port, &devlink->port_list, list) {
 			list_for_each_entry(param_item,
@@ -4841,12 +4916,15 @@ static int devlink_nl_cmd_port_param_get_dumpit(struct sk_buff *msg,
 					err = 0;
 				} else if (err) {
 					mutex_unlock(&devlink->lock);
+					devlink_put(devlink);
 					goto out;
 				}
 				idx++;
 			}
 		}
 		mutex_unlock(&devlink->lock);
+retry:
+		devlink_put(devlink);
 	}
 out:
 	mutex_unlock(&devlink_mutex);
@@ -5385,14 +5463,20 @@ static int devlink_nl_cmd_region_get_dumpit(struct sk_buff *msg,
 	struct devlink *devlink;
 	int start = cb->args[0];
 	int idx = 0;
-	int err;
+	int err = 0;
 
 	mutex_lock(&devlink_mutex);
 	list_for_each_entry(devlink, &devlink_list, list) {
-		if (!net_eq(devlink_net(devlink), sock_net(msg->sk)))
+		if (!devlink_try_get(devlink))
 			continue;
+
+		if (!net_eq(devlink_net(devlink), sock_net(msg->sk)))
+			goto retry;
+
 		err = devlink_nl_cmd_region_get_devlink_dumpit(msg, cb, devlink,
 							       &idx, start);
+retry:
+		devlink_put(devlink);
 		if (err)
 			goto out;
 	}
@@ -5755,6 +5839,7 @@ static int devlink_nl_cmd_region_read_dumpit(struct sk_buff *skb,
 	nla_nest_end(skb, chunks_attr);
 	genlmsg_end(skb, hdr);
 	mutex_unlock(&devlink->lock);
+	devlink_put(devlink);
 	mutex_unlock(&devlink_mutex);
 
 	return skb->len;
@@ -5763,6 +5848,7 @@ nla_put_failure:
 	genlmsg_cancel(skb, hdr);
 out_unlock:
 	mutex_unlock(&devlink->lock);
+	devlink_put(devlink);
 out_dev:
 	mutex_unlock(&devlink_mutex);
 	return err;
@@ -5914,17 +6000,14 @@ static int devlink_nl_cmd_info_get_dumpit(struct sk_buff *msg,
 
 	mutex_lock(&devlink_mutex);
 	list_for_each_entry(devlink, &devlink_list, list) {
-		if (!net_eq(devlink_net(devlink), sock_net(msg->sk)))
+		if (!devlink_try_get(devlink))
 			continue;
-		if (idx < start) {
-			idx++;
-			continue;
-		}
 
-		if (!devlink->ops->info_get) {
-			idx++;
-			continue;
-		}
+		if (!net_eq(devlink_net(devlink), sock_net(msg->sk)))
+			goto retry;
+
+		if (idx < start || !devlink->ops->info_get)
+			goto inc;
 
 		mutex_lock(&devlink->lock);
 		err = devlink_nl_info_fill(msg, devlink, DEVLINK_CMD_INFO_GET,
@@ -5934,9 +6017,14 @@ static int devlink_nl_cmd_info_get_dumpit(struct sk_buff *msg,
 		mutex_unlock(&devlink->lock);
 		if (err == -EOPNOTSUPP)
 			err = 0;
-		else if (err)
+		else if (err) {
+			devlink_put(devlink);
 			break;
+		}
+inc:
 		idx++;
+retry:
+		devlink_put(devlink);
 	}
 	mutex_unlock(&devlink_mutex);
 
@@ -7021,6 +7109,7 @@ devlink_health_reporter_get_from_cb(struct netlink_callback *cb)
 		goto unlock;
 
 	reporter = devlink_health_reporter_get_from_attrs(devlink, attrs);
+	devlink_put(devlink);
 	mutex_unlock(&devlink_mutex);
 	return reporter;
 unlock:
@@ -7092,8 +7181,12 @@ devlink_nl_cmd_health_reporter_get_dumpit(struct sk_buff *msg,
 
 	mutex_lock(&devlink_mutex);
 	list_for_each_entry(devlink, &devlink_list, list) {
-		if (!net_eq(devlink_net(devlink), sock_net(msg->sk)))
+		if (!devlink_try_get(devlink))
 			continue;
+
+		if (!net_eq(devlink_net(devlink), sock_net(msg->sk)))
+			goto retry_rep;
+
 		mutex_lock(&devlink->reporters_lock);
 		list_for_each_entry(reporter, &devlink->reporter_list,
 				    list) {
@@ -7107,16 +7200,23 @@ devlink_nl_cmd_health_reporter_get_dumpit(struct sk_buff *msg,
 				NLM_F_MULTI);
 			if (err) {
 				mutex_unlock(&devlink->reporters_lock);
+				devlink_put(devlink);
 				goto out;
 			}
 			idx++;
 		}
 		mutex_unlock(&devlink->reporters_lock);
+retry_rep:
+		devlink_put(devlink);
 	}
 
 	list_for_each_entry(devlink, &devlink_list, list) {
-		if (!net_eq(devlink_net(devlink), sock_net(msg->sk)))
+		if (!devlink_try_get(devlink))
 			continue;
+
+		if (!net_eq(devlink_net(devlink), sock_net(msg->sk)))
+			goto retry_port;
+
 		mutex_lock(&devlink->lock);
 		list_for_each_entry(port, &devlink->port_list, list) {
 			mutex_lock(&port->reporters_lock);
@@ -7133,6 +7233,7 @@ devlink_nl_cmd_health_reporter_get_dumpit(struct sk_buff *msg,
 				if (err) {
 					mutex_unlock(&port->reporters_lock);
 					mutex_unlock(&devlink->lock);
+					devlink_put(devlink);
 					goto out;
 				}
 				idx++;
@@ -7140,6 +7241,8 @@ devlink_nl_cmd_health_reporter_get_dumpit(struct sk_buff *msg,
 			mutex_unlock(&port->reporters_lock);
 		}
 		mutex_unlock(&devlink->lock);
+retry_port:
+		devlink_put(devlink);
 	}
 out:
 	mutex_unlock(&devlink_mutex);
@@ -7673,8 +7776,12 @@ static int devlink_nl_cmd_trap_get_dumpit(struct sk_buff *msg,
 
 	mutex_lock(&devlink_mutex);
 	list_for_each_entry(devlink, &devlink_list, list) {
-		if (!net_eq(devlink_net(devlink), sock_net(msg->sk)))
+		if (!devlink_try_get(devlink))
 			continue;
+
+		if (!net_eq(devlink_net(devlink), sock_net(msg->sk)))
+			goto retry;
+
 		mutex_lock(&devlink->lock);
 		list_for_each_entry(trap_item, &devlink->trap_list, list) {
 			if (idx < start) {
@@ -7688,11 +7795,14 @@ static int devlink_nl_cmd_trap_get_dumpit(struct sk_buff *msg,
 						   NLM_F_MULTI);
 			if (err) {
 				mutex_unlock(&devlink->lock);
+				devlink_put(devlink);
 				goto out;
 			}
 			idx++;
 		}
 		mutex_unlock(&devlink->lock);
+retry:
+		devlink_put(devlink);
 	}
 out:
 	mutex_unlock(&devlink_mutex);
@@ -7892,8 +8002,12 @@ static int devlink_nl_cmd_trap_group_get_dumpit(struct sk_buff *msg,
 
 	mutex_lock(&devlink_mutex);
 	list_for_each_entry(devlink, &devlink_list, list) {
-		if (!net_eq(devlink_net(devlink), sock_net(msg->sk)))
+		if (!devlink_try_get(devlink))
 			continue;
+
+		if (!net_eq(devlink_net(devlink), sock_net(msg->sk)))
+			goto retry;
+
 		mutex_lock(&devlink->lock);
 		list_for_each_entry(group_item, &devlink->trap_group_list,
 				    list) {
@@ -7908,11 +8022,14 @@ static int devlink_nl_cmd_trap_group_get_dumpit(struct sk_buff *msg,
 							 NLM_F_MULTI);
 			if (err) {
 				mutex_unlock(&devlink->lock);
+				devlink_put(devlink);
 				goto out;
 			}
 			idx++;
 		}
 		mutex_unlock(&devlink->lock);
+retry:
+		devlink_put(devlink);
 	}
 out:
 	mutex_unlock(&devlink_mutex);
@@ -8198,8 +8315,12 @@ static int devlink_nl_cmd_trap_policer_get_dumpit(struct sk_buff *msg,
 
 	mutex_lock(&devlink_mutex);
 	list_for_each_entry(devlink, &devlink_list, list) {
-		if (!net_eq(devlink_net(devlink), sock_net(msg->sk)))
+		if (!devlink_try_get(devlink))
 			continue;
+
+		if (!net_eq(devlink_net(devlink), sock_net(msg->sk)))
+			goto retry;
+
 		mutex_lock(&devlink->lock);
 		list_for_each_entry(policer_item, &devlink->trap_policer_list,
 				    list) {
@@ -8214,11 +8335,14 @@ static int devlink_nl_cmd_trap_policer_get_dumpit(struct sk_buff *msg,
 							   NLM_F_MULTI);
 			if (err) {
 				mutex_unlock(&devlink->lock);
+				devlink_put(devlink);
 				goto out;
 			}
 			idx++;
 		}
 		mutex_unlock(&devlink->lock);
+retry:
+		devlink_put(devlink);
 	}
 out:
 	mutex_unlock(&devlink_mutex);
@@ -8801,6 +8925,9 @@ struct devlink *devlink_alloc_ns(const struct devlink_ops *ops,
 	INIT_LIST_HEAD(&devlink->trap_policer_list);
 	mutex_init(&devlink->lock);
 	mutex_init(&devlink->reporters_lock);
+	refcount_set(&devlink->refcount, 1);
+	init_completion(&devlink->comp);
+
 	return devlink;
 }
 EXPORT_SYMBOL_GPL(devlink_alloc_ns);
@@ -8827,6 +8954,9 @@ EXPORT_SYMBOL_GPL(devlink_register);
  */
 void devlink_unregister(struct devlink *devlink)
 {
+	devlink_put(devlink);
+	wait_for_completion(&devlink->comp);
+
 	mutex_lock(&devlink_mutex);
 	WARN_ON(devlink_reload_supported(devlink->ops) &&
 		devlink->reload_enabled);
@@ -11374,9 +11504,12 @@ static void __net_exit devlink_pernet_pre_exit(struct net *net)
 	 */
 	mutex_lock(&devlink_mutex);
 	list_for_each_entry(devlink, &devlink_list, list) {
-		if (!net_eq(devlink_net(devlink), net))
+		if (!devlink_try_get(devlink))
 			continue;
 
+		if (!net_eq(devlink_net(devlink), net))
+			goto retry;
+
 		WARN_ON(!devlink_reload_supported(devlink->ops));
 		err = devlink_reload(devlink, &init_net,
 				     DEVLINK_RELOAD_ACTION_DRIVER_REINIT,
@@ -11384,6 +11517,8 @@ static void __net_exit devlink_pernet_pre_exit(struct net *net)
 				     &actions_performed, NULL);
 		if (err && err != -EOPNOTSUPP)
 			pr_warn("Failed to reload devlink instance into init_net\n");
+retry:
+		devlink_put(devlink);
 	}
 	mutex_unlock(&devlink_mutex);
 }