devlink: Hang reporter's dump method on a dumpit cb

The devlink health reporter provides a dump method on an error. Dump
may contain a large amount of data, in this case doit cb isn't sufficient.
This is because the user side is blocking and doesn't allow draining of
the socket until the socket runs out of buffers. Using dumpit cb
is the correct way to go.
Please note that thankfully the dump op is not yet implemented in any
driver and therefore this change is not breaking userspace.

Fixes: 35455e23e6 ("devlink: Add health dump {get,clear} commands")
Signed-off-by: Aya Levin <ayal@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>

net/core/devlink.c

@@ -4518,6 +4518,35 @@ nla_put_failure:
 	return err;
 }
 
+static int devlink_fmsg_dumpit(struct devlink_fmsg *fmsg, struct sk_buff *skb,
+			       struct netlink_callback *cb,
+			       enum devlink_command cmd)
+{
+	int index = cb->args[0];
+	int tmp_index = index;
+	void *hdr;
+	int err;
+
+	hdr = genlmsg_put(skb, NETLINK_CB(cb->skb).portid, cb->nlh->nlmsg_seq,
+			  &devlink_nl_family, NLM_F_ACK | NLM_F_MULTI, cmd);
+	if (!hdr) {
+		err = -EMSGSIZE;
+		goto nla_put_failure;
+	}
+
+	err = devlink_fmsg_prepare_skb(fmsg, skb, &index);
+	if ((err && err != -EMSGSIZE) || tmp_index == index)
+		goto nla_put_failure;
+
+	cb->args[0] = index;
+	genlmsg_end(skb, hdr);
+	return skb->len;
+
+nla_put_failure:
+	genlmsg_cancel(skb, hdr);
+	return err;
+}
+
 struct devlink_health_reporter {
 	struct list_head list;
 	void *priv;
@@ -4750,17 +4779,16 @@ int devlink_health_report(struct devlink_health_reporter *reporter,
 EXPORT_SYMBOL_GPL(devlink_health_report);
 
 static struct devlink_health_reporter *
-devlink_health_reporter_get_from_info(struct devlink *devlink,
-				      struct genl_info *info)
+devlink_health_reporter_get_from_attrs(struct devlink *devlink,
+				       struct nlattr **attrs)
 {
 	struct devlink_health_reporter *reporter;
 	char *reporter_name;
 
-	if (!info->attrs[DEVLINK_ATTR_HEALTH_REPORTER_NAME])
+	if (!attrs[DEVLINK_ATTR_HEALTH_REPORTER_NAME])
 		return NULL;
 
-	reporter_name =
-		nla_data(info->attrs[DEVLINK_ATTR_HEALTH_REPORTER_NAME]);
+	reporter_name = nla_data(attrs[DEVLINK_ATTR_HEALTH_REPORTER_NAME]);
 	mutex_lock(&devlink->reporters_lock);
 	reporter = devlink_health_reporter_find_by_name(devlink, reporter_name);
 	if (reporter)
@@ -4769,6 +4797,48 @@ devlink_health_reporter_get_from_info(struct devlink *devlink,
 	return reporter;
 }
 
+static struct devlink_health_reporter *
+devlink_health_reporter_get_from_info(struct devlink *devlink,
+				      struct genl_info *info)
+{
+	return devlink_health_reporter_get_from_attrs(devlink, info->attrs);
+}
+
+static struct devlink_health_reporter *
+devlink_health_reporter_get_from_cb(struct netlink_callback *cb)
+{
+	struct devlink_health_reporter *reporter;
+	struct devlink *devlink;
+	struct nlattr **attrs;
+	int err;
+
+	attrs = kmalloc_array(DEVLINK_ATTR_MAX + 1, sizeof(*attrs), GFP_KERNEL);
+	if (!attrs)
+		return NULL;
+
+	err = nlmsg_parse_deprecated(cb->nlh,
+				     GENL_HDRLEN + devlink_nl_family.hdrsize,
+				     attrs, DEVLINK_ATTR_MAX,
+				     devlink_nl_family.policy, cb->extack);
+	if (err)
+		goto free;
+
+	mutex_lock(&devlink_mutex);
+	devlink = devlink_get_from_attrs(sock_net(cb->skb->sk), attrs);
+	if (IS_ERR(devlink))
+		goto unlock;
+
+	reporter = devlink_health_reporter_get_from_attrs(devlink, attrs);
+	mutex_unlock(&devlink_mutex);
+	kfree(attrs);
+	return reporter;
+unlock:
+	mutex_unlock(&devlink_mutex);
+free:
+	kfree(attrs);
+	return NULL;
+}
+
 static void
 devlink_health_reporter_put(struct devlink_health_reporter *reporter)
 {
@@ -5004,32 +5074,40 @@ out:
 	return err;
 }
 
-static int devlink_nl_cmd_health_reporter_dump_get_doit(struct sk_buff *skb,
-							struct genl_info *info)
+static int
+devlink_nl_cmd_health_reporter_dump_get_dumpit(struct sk_buff *skb,
+					       struct netlink_callback *cb)
 {
-	struct devlink *devlink = info->user_ptr[0];
 	struct devlink_health_reporter *reporter;
+	u64 start = cb->args[0];
 	int err;
 
-	reporter = devlink_health_reporter_get_from_info(devlink, info);
+	reporter = devlink_health_reporter_get_from_cb(cb);
 	if (!reporter)
 		return -EINVAL;
 
 	if (!reporter->ops->dump) {
-		devlink_health_reporter_put(reporter);
-		return -EOPNOTSUPP;
+		err = -EOPNOTSUPP;
+		goto out;
+	}
+	mutex_lock(&reporter->dump_lock);
+	if (!start) {
+		err = devlink_health_do_dump(reporter, NULL);
+		if (err)
+			goto unlock;
+		cb->args[1] = reporter->dump_ts;
+	}
+	if (!reporter->dump_fmsg || cb->args[1] != reporter->dump_ts) {
+		NL_SET_ERR_MSG_MOD(cb->extack, "Dump trampled, please retry");
+		err = -EAGAIN;
+		goto unlock;
 	}
 
-	mutex_lock(&reporter->dump_lock);
-	err = devlink_health_do_dump(reporter, NULL);
-	if (err)
-		goto out;
-
-	err = devlink_fmsg_snd(reporter->dump_fmsg, info,
-			       DEVLINK_CMD_HEALTH_REPORTER_DUMP_GET, 0);
-
-out:
+	err = devlink_fmsg_dumpit(reporter->dump_fmsg, skb, cb,
+				  DEVLINK_CMD_HEALTH_REPORTER_DUMP_GET);
+unlock:
 	mutex_unlock(&reporter->dump_lock);
+out:
 	devlink_health_reporter_put(reporter);
 	return err;
 }
@@ -5366,7 +5444,7 @@ static const struct genl_ops devlink_nl_ops[] = {
 	{
 		.cmd = DEVLINK_CMD_HEALTH_REPORTER_DUMP_GET,
 		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
-		.doit = devlink_nl_cmd_health_reporter_dump_get_doit,
+		.dumpit = devlink_nl_cmd_health_reporter_dump_get_dumpit,
 		.flags = GENL_ADMIN_PERM,
 		.internal_flags = DEVLINK_NL_FLAG_NEED_DEVLINK |
 				  DEVLINK_NL_FLAG_NO_LOCK,