From fd9ea57f4e9514f9d0f0dec505eefd99a8faa148 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 8 Jun 2022 09:04:38 -0700 Subject: [PATCH] net: add napi_get_frags_check() helper This is a follow up of commit 3226b158e67c ("net: avoid 32 x truesize under-estimation for tiny skbs") When/if we increase MAX_SKB_FRAGS, we better make sure the old bug will not come back. Adding a check in napi_get_frags() would be costly, even if using DEBUG_NET_WARN_ON_ONCE(). Signed-off-by: Eric Dumazet Signed-off-by: Jakub Kicinski --- net/core/dev.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/net/core/dev.c b/net/core/dev.c index 39cb905..8958c42 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -6351,6 +6351,23 @@ int dev_set_threaded(struct net_device *dev, bool threaded) } EXPORT_SYMBOL(dev_set_threaded); +/* Double check that napi_get_frags() allocates skbs with + * skb->head being backed by slab, not a page fragment. + * This is to make sure bug fixed in 3226b158e67c + * ("net: avoid 32 x truesize under-estimation for tiny skbs") + * does not accidentally come back. + */ +static void napi_get_frags_check(struct napi_struct *napi) +{ + struct sk_buff *skb; + + local_bh_disable(); + skb = napi_get_frags(napi); + WARN_ON_ONCE(skb && skb->head_frag); + napi_free_frags(napi); + local_bh_enable(); +} + void netif_napi_add_weight(struct net_device *dev, struct napi_struct *napi, int (*poll)(struct napi_struct *, int), int weight) { @@ -6378,6 +6395,7 @@ void netif_napi_add_weight(struct net_device *dev, struct napi_struct *napi, set_bit(NAPI_STATE_NPSVC, &napi->state); list_add_rcu(&napi->dev_list, &dev->napi_list); napi_hash_add(napi); + napi_get_frags_check(napi); /* Create kthread for this napi if dev->threaded is set. * Clear dev->threaded if kthread creation failed so that * threaded mode will not be enabled in napi_enable(). -- 2.7.4