From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pablo Neira Ayuso Subject: Re: [PATCH nf-next v2 1/1] netfilter: helper: Remove useless rcu lock when get expectfn Date: Wed, 29 Mar 2017 12:44:12 +0200 Message-ID: <20170329104412.GA6337@salvia> References: <1490148902-96508-1-git-send-email-gfree.wind@foxmail.com> <20170329100730.GA4131@salvia> <000301d2a877$4e174c50$ea45e4f0$@foxmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: netfilter-devel@vger.kernel.org, 'Gao Feng' To: Gao Feng Return-path: Received: from mail.us.es ([193.147.175.20]:55772 "EHLO mail.us.es" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752092AbdC2KoT (ORCPT ); Wed, 29 Mar 2017 06:44:19 -0400 Received: from antivirus1-rhel7.int (unknown [192.168.2.11]) by mail.us.es (Postfix) with ESMTP id B2C91BA1B3 for ; Wed, 29 Mar 2017 12:44:15 +0200 (CEST) Received: from antivirus1-rhel7.int (localhost [127.0.0.1]) by antivirus1-rhel7.int (Postfix) with ESMTP id A1D18DA877 for ; Wed, 29 Mar 2017 12:44:15 +0200 (CEST) Received: from antivirus1-rhel7.int (localhost [127.0.0.1]) by antivirus1-rhel7.int (Postfix) with ESMTP id DBCECDA87D for ; Wed, 29 Mar 2017 12:44:11 +0200 (CEST) Content-Disposition: inline In-Reply-To: <000301d2a877$4e174c50$ea45e4f0$@foxmail.com> Sender: netfilter-devel-owner@vger.kernel.org List-ID: On Wed, Mar 29, 2017 at 06:29:10PM +0800, Gao Feng wrote: > Hi Pablo, > > > -----Original Message----- > > From: Pablo Neira Ayuso [mailto:pablo@netfilter.org] > > Sent: Wednesday, March 29, 2017 6:08 PM > > To: gfree.wind@foxmail.com > > Cc: netfilter-devel@vger.kernel.org; Gao Feng > > Subject: Re: [PATCH nf-next v2 1/1] netfilter: helper: Remove useless rcu > lock > > when get expectfn > > > > On Wed, Mar 22, 2017 at 10:15:02AM +0800, gfree.wind@foxmail.com wrote: > > > From: Gao Feng > > > > > > Because these two functions return the nf_ct_helper_expectfn pointer > > > which should be protected by rcu lock. So it should makes sure the > > > caller should hold the rcu lock, not inside these functions. > > > > > > Signed-off-by: Gao Feng > > > --- > > > v2: Shorter subject, per Pablo > > > v1: Initial version > > > > > > net/netfilter/nf_conntrack_helper.c | 6 ++---- > > > 1 file changed, 2 insertions(+), 4 deletions(-) > > > > > > diff --git a/net/netfilter/nf_conntrack_helper.c > > > b/net/netfilter/nf_conntrack_helper.c > > > index 6dc44d9..bce3d1f 100644 > > > --- a/net/netfilter/nf_conntrack_helper.c > > > +++ b/net/netfilter/nf_conntrack_helper.c > > > @@ -311,38 +311,36 @@ void nf_ct_helper_expectfn_unregister(struct > > > nf_ct_helper_expectfn *n) } > > > EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister); > > > > > > +/* Caller should hold the rcu lock */ > > > struct nf_ct_helper_expectfn * > > > nf_ct_helper_expectfn_find_by_name(const char *name) { > > > struct nf_ct_helper_expectfn *cur; > > > bool found = false; > > > > > > - rcu_read_lock(); > > > list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) { > > > if (!strcmp(cur->name, name)) { > > > found = true; > > > break; > > > } > > > } > > > - rcu_read_unlock(); > > > return found ? cur : NULL; > > > } > > > EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name); > > > > nf_ct_helper_expectfn_find_by_name() is called from ctnetlink, via > > ctnetlink_create_expect() and rcu read side lock is not held there. > There are two reasons. > 1. The rcu lock would be added in my patch " netfilter: helper: Add the rcu > lock when call __nf_conntrack_helper_find" for nf > https://patchwork.ozlabs.org/patch/741865/. If you have interdependencies between two patches like this, it's better to make it in one single go. > So the ctnetlink_create_expect would hold the rcu lock after apply that > patch. > > 2. Because these two functions return one pointer which needs RCU lock, so > the caller must hold rcu lock. > Or it still meets one error even though there is one rcu lock in these two > functions. > Because the memory which the returned pointer point to would be freed > already after rcu_read_unlock. > So the rcu lock is unnecessary in these functions. That's right. You're fixing up a real problem, no doubt. I'm just questioning that I think that if you are fixing up rcu locking, which seems to be the case, you just do it in one single patch. Thanks!