net: disable netpoll on fresh napis

stable inclusion
from linux-4.19.145
commit 9f313bcb3b3d021f9b2f04f6d8464f8e9e309452

--------------------------------

[ Upstream commit 96e97bc0 ]

napi_disable() makes sure to set the NAPI_STATE_NPSVC bit to prevent
netpoll from accessing rings before init is complete. However, the
same is not done for fresh napi instances in netif_napi_add(),
even though we expect NAPI instances to be added as disabled.

This causes crashes during driver reconfiguration (enabling XDP,
changing the channel count) - if there is any printk() after
netif_napi_add() but before napi_enable().

To ensure memory ordering is correct we need to use RCU accessors.
Reported-by: NRob Sherwood <rsher@fb.com>
Fixes: 2d8bff12 ("netpoll: Close race condition between poll_one_napi and napi_disable")
Signed-off-by: NJakub Kicinski <kuba@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>
Signed-off-by: NAichun Li <liaichun@huawei.com>
Reviewed-by: Nwangxiaopeng <wangxiaopeng7@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

net/core/dev.c

@@ -6196,12 +6196,13 @@ void netif_napi_add(struct net_device *dev, struct napi_struct *napi,
 		pr_err_once("netif_napi_add() called with weight %d on device %s\n",
 			    weight, dev->name);
 	napi->weight = weight;
-	list_add(&napi->dev_list, &dev->napi_list);
 	napi->dev = dev;
 #ifdef CONFIG_NETPOLL
 	napi->poll_owner = -1;
 #endif
 	set_bit(NAPI_STATE_SCHED, &napi->state);
+	set_bit(NAPI_STATE_NPSVC, &napi->state);
+	list_add_rcu(&napi->dev_list, &dev->napi_list);
 	napi_hash_add(napi);
 }
 EXPORT_SYMBOL(netif_napi_add);

net/core/netpoll.c

@@ -161,7 +161,7 @@ static void poll_napi(struct net_device *dev)
 	struct napi_struct *napi;
 	int cpu = smp_processor_id();
 
-	list_for_each_entry(napi, &dev->napi_list, dev_list) {
+	list_for_each_entry_rcu(napi, &dev->napi_list, dev_list) {
 		if (cmpxchg(&napi->poll_owner, -1, cpu) == -1) {
 			poll_one_napi(napi);
 			smp_store_release(&napi->poll_owner, -1);