[RFC net 2/2] netdev-genl: Hold rcu_read_lock in napi_set

[Joe Damato <jdamato@fastly.com>]

Hold rcu_read_lock during netdev_nl_napi_set_doit, which calls
napi_by_id and requires rcu_read_lock to be held.

Add a helper function which calls napi_by_id and sets the error code and
extack. It is used by this commit and the next commit to reduce code
duplication.

Closes: https://lore.kernel.org/netdev/719083c2-e277-447b-b6ea-ca3acb293a03@redhat.com/
Fixes: 1287c1ae0fc2 ("netdev-genl: Support setting per-NAPI config values")
Signed-off-by: Joe Damato <jdamato@fastly.com>
---
 net/core/netdev-genl.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/net/core/netdev-genl.c b/net/core/netdev-genl.c
index 934c63a93524..2a04270e9d2d 100644
--- a/net/core/netdev-genl.c
+++ b/net/core/netdev-genl.c
@@ -361,15 +361,13 @@ int netdev_nl_napi_set_doit(struct sk_buff *skb, struct genl_info *info)
 	napi_id = nla_get_u32(info->attrs[NETDEV_A_NAPI_ID]);
 
 	rtnl_lock();
+	rcu_read_lock();
 
-	napi = napi_by_id(napi_id);
-	if (napi) {
+	napi = __do_napi_by_id(napi_id, info, &err);
+	if (!err)
 		err = netdev_nl_napi_set_config(napi, info);
-	} else {
-		NL_SET_BAD_ATTR(info->extack, info->attrs[NETDEV_A_NAPI_ID]);
-		err = -ENOENT;
-	}
 
+	rcu_read_unlock();
 	rtnl_unlock();
 
 	return err;
-- 
2.25.1