net: disable netpoll on fresh napis

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: Rob Sherwood <rsher@fb.com>
Fixes: 8df8097a7ef9 ("netpoll: Close race condition between poll_one_napi and napi_disable")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/dev.c b/net/core/dev.c
index d42c9ea0c3c03764816d02bcdccc668f61042284..95ac7568f6932a250f89ea3e73bf4c542810ce80 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6612,12 +6612,13 @@ void netif_napi_add(struct net_device *dev, struct napi_struct *napi,
                netdev_err_once(dev, "%s() called with weight %d\n", __func__,
                                weight);
        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);

diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index 093e90e52bc25411806fe2f3d04ca27cab47ec32..2338753e936b7188d7d0ccb350cee8a34dd88172 100644 (file)
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -162,7 +162,7 @@ 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);