> -----邮件原件----- > 发件人: Eric Dumazet [mailto:eric.dumazet@xxxxxxxxx] > 发送时间: 2019年2月25日 11:50 > 收件人: Li,Rongqing <lirongqing@xxxxxxxxx>; netfilter-devel@xxxxxxxxxxxxxxx > 主题: Re: [PATCH] netfilter: force access of RCU protected data in > nft_update_chain_stats > > > > On 02/24/2019 05:58 PM, Li RongQing wrote: > > basechain->stats is rcu protected data, cannot assure that > > twice accesses have the same result, so dereference it once. > > > > basechain->stats is allocated by percpu allocater, if it is not NULL, > > its percpu variable does not need to be checked with NULL > > > > Signed-off-by: Zhang Yu <zhangyu31@xxxxxxxxx> > > Signed-off-by: Li RongQing <lirongqing@xxxxxxxxx> > > --- > > net/netfilter/nf_tables_core.c | 18 +++++++++--------- > > 1 file changed, 9 insertions(+), 9 deletions(-) > > > > diff --git a/net/netfilter/nf_tables_core.c > > b/net/netfilter/nf_tables_core.c index 2a00aef7b6d4..9be622c76a62 > > 100644 > > --- a/net/netfilter/nf_tables_core.c > > +++ b/net/netfilter/nf_tables_core.c > > @@ -98,20 +98,20 @@ static noinline void nft_update_chain_stats(const > struct nft_chain *chain, > > const struct nft_pktinfo *pkt) { > > struct nft_base_chain *base_chain; > > - struct nft_stats *stats; > > + struct nft_stats *stats, *pstat; > > > > base_chain = nft_base_chain(chain); > > - if (!rcu_access_pointer(base_chain->stats)) > > + > > + stats = rcu_dereference(base_chain->stats); > > This looks bogus to me. > > Where is the needed rcu_read_lock() before rcu_dereference() ? > Ok, I will check it carefully. > This rcu_access_pointer() test is fine, and avoids a > local_bh_disable()/local_bh_enable() > if they are not needed. But it can not assure that rcu_dereference(base_chain->stats) returns NULL since nft_chain_stats_replace, should we check it again, other than check the returning of this_cpu_ptr? thanks -RongQing
