From: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
To: Jakub Kicinski <kuba@kernel.org>
Cc: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>,
sfr@canb.auug.org.au, Amol Grover <frextrite@gmail.com>,
"David S . Miller" <davem@davemloft.net>,
Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-kernel-mentees@lists.linuxfoundation.org,
Joel Fernandes <joel@joelfernandes.org>,
"Paul E . McKenney" <paulmck@kernel.org>
Subject: Re: [PATCH net 2/2 RESEND] ipmr: Add lockdep expression to ipmr_for_each_table macro
Date: Wed, 13 May 2020 11:04:57 +0530 [thread overview]
Message-ID: <20200513053457.GA13541@madhuparna-HP-Notebook> (raw)
In-Reply-To: <20200512093231.7ce29f30@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
On Tue, May 12, 2020 at 09:32:31AM -0700, Jakub Kicinski wrote:
> On Tue, 12 May 2020 10:47:05 +0530 Madhuparna Bhowmik wrote:
> > > > #ifdef CONFIG_IP_MROUTE_MULTIPLE_TABLES
> > > > -#define ipmr_for_each_table(mrt, net) \
> > > > - list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list, \
> > > > - lockdep_rtnl_is_held())
> > > > +#define ipmr_for_each_table(mrt, net) \
> > > > + list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list, \
> > > > + lockdep_rtnl_is_held() || \
> > > > + lockdep_is_held(&pernet_ops_rwsem))
> > >
> > > This is a strange condition, IMHO. How can we be fine with either
> > > lock.. This is supposed to be the writer side lock, one can't have
> > > two writer side locks..
> > >
> > > I think what is happening is this:
> > >
> > > ipmr_net_init() -> ipmr_rules_init() -> ipmr_new_table()
> > >
> > > ipmr_new_table() returns an existing table if there is one, but
> > > obviously none can exist at init. So a better fix would be:
> > >
> > > #define ipmr_for_each_table(mrt, net) \
> > > list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list, \
> > > lockdep_rtnl_is_held() || \
> > > list_empty(&net->ipv4.mr_tables))
> > >
> > (adding Stephen)
> >
> > Hi Jakub,
> >
> > Thank you for your suggestion about this patch.
> > Here is a stack trace for ipmr.c:
> >
> > [...]
>
> Thanks!
>
> > > Thoughts?
> >
> > Do you think a similar fix (the one you suggested) is also applicable
> > in the ip6mr case.
>
> Yes, looking at the code it seems ip6mr has the exact same flow for
> netns init.
Alright, thanks a lot.
I will send a patch for ip6mr.c soon.
Thank you,
Madhuparna
next prev parent reply other threads:[~2020-05-13 5:35 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-09 7:22 [PATCH net 1/2 RESEND] ipmr: Fix RCU list debugging warning Amol Grover
2020-05-09 7:22 ` [PATCH net 2/2 RESEND] ipmr: Add lockdep expression to ipmr_for_each_table macro Amol Grover
2020-05-09 21:19 ` Jakub Kicinski
2020-05-12 5:17 ` Madhuparna Bhowmik
2020-05-12 16:32 ` Jakub Kicinski
2020-05-13 5:34 ` Madhuparna Bhowmik [this message]
2020-05-12 17:17 ` Amol Grover
2020-05-12 21:59 ` Jakub Kicinski
2020-05-13 11:54 ` Stephen Rothwell
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