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Date: Tue, 12 May 2020 09:32:31 -0700 From: Jakub Kicinski <kuba@...nel.org> To: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com> Cc: sfr@...b.auug.org.au, Amol Grover <frextrite@...il.com>, "David S . Miller" <davem@...emloft.net>, Alexey Kuznetsov <kuznet@....inr.ac.ru>, Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, linux-kernel-mentees@...ts.linuxfoundation.org, Joel Fernandes <joel@...lfernandes.org>, "Paul E . McKenney" <paulmck@...nel.org> Subject: Re: [PATCH net 2/2 RESEND] ipmr: Add lockdep expression to ipmr_for_each_table macro 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.
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