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[73.241.150.70]) by smtp.gmail.com with ESMTPSA id 79sm998388ywr.110.2019.02.24.19.50.09 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 24 Feb 2019 19:50:09 -0800 (PST) Subject: Re: [PATCH] netfilter: force access of RCU protected data in nft_update_chain_stats To: Li RongQing , netfilter-devel@vger.kernel.org References: <1551059920-14120-1-git-send-email-lirongqing@baidu.com> From: Eric Dumazet Message-ID: <4818220f-1c66-df00-e397-4efbeba82665@gmail.com> Date: Sun, 24 Feb 2019 19:50:08 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <1551059920-14120-1-git-send-email-lirongqing@baidu.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: netfilter-devel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netfilter-devel@vger.kernel.org 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 > Signed-off-by: Li RongQing > --- > 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() ? This rcu_access_pointer() test is fine, and avoids a local_bh_disable()/local_bh_enable() if they are not needed. > + if (!stats) > return; > > local_bh_disable(); > - stats = this_cpu_ptr(rcu_dereference(base_chain->stats)); > - if (stats) { > - u64_stats_update_begin(&stats->syncp); > - stats->pkts++; > - stats->bytes += pkt->skb->len; > - u64_stats_update_end(&stats->syncp); > - } > + pstat = this_cpu_ptr(stats); > + u64_stats_update_begin(&pstat->syncp); > + pstat->pkts++; > + pstat->bytes += pkt->skb->len; > + u64_stats_update_end(&pstat->syncp); > local_bh_enable(); > } > >