From: Jakub Kicinski <kuba@kernel.org> To: Amol Grover <frextrite@gmail.com> Cc: "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>, Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>, "Paul E . McKenney" <paulmck@kernel.org> Subject: Re: [PATCH net 2/2 RESEND] ipmr: Add lockdep expression to ipmr_for_each_table macro Date: Sat, 9 May 2020 14:19:38 -0700 [thread overview] Message-ID: <20200509141938.028fa959@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> (raw) In-Reply-To: <20200509072243.3141-2-frextrite@gmail.com> On Sat, 9 May 2020 12:52:44 +0530 Amol Grover wrote: > ipmr_for_each_table() uses list_for_each_entry_rcu() for > traversing outside of an RCU read-side critical section but > under the protection of pernet_ops_rwsem. Hence add the > corresponding lockdep expression to silence the following > false-positive warning at boot: Thanks for the fix, the warning has been annoying me as well! > [ 0.645292] ============================= > [ 0.645294] WARNING: suspicious RCU usage > [ 0.645296] 5.5.4-stable #17 Not tainted > [ 0.645297] ----------------------------- > [ 0.645299] net/ipv4/ipmr.c:136 RCU-list traversed in non-reader section!! please provide a fuller stack trace, it would have helped the review > Signed-off-by: Amol Grover <frextrite@gmail.com> > --- > net/ipv4/ipmr.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c > index 99c864eb6e34..950ffe9943da 100644 > --- a/net/ipv4/ipmr.c > +++ b/net/ipv4/ipmr.c > @@ -109,9 +109,10 @@ static void mroute_clean_tables(struct mr_table *mrt, int flags); > static void ipmr_expire_process(struct timer_list *t); > > #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)) Thoughts?
WARNING: multiple messages have this Message-ID (diff)
From: Jakub Kicinski <kuba@kernel.org> To: Amol Grover <frextrite@gmail.com> Cc: "Paul E . McKenney" <paulmck@kernel.org>, Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>, Joel Fernandes <joel@joelfernandes.org>, Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>, linux-kernel-mentees@lists.linuxfoundation.org, "David S . Miller" <davem@davemloft.net> Subject: Re: [Linux-kernel-mentees] [PATCH net 2/2 RESEND] ipmr: Add lockdep expression to ipmr_for_each_table macro Date: Sat, 9 May 2020 14:19:38 -0700 [thread overview] Message-ID: <20200509141938.028fa959@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> (raw) In-Reply-To: <20200509072243.3141-2-frextrite@gmail.com> On Sat, 9 May 2020 12:52:44 +0530 Amol Grover wrote: > ipmr_for_each_table() uses list_for_each_entry_rcu() for > traversing outside of an RCU read-side critical section but > under the protection of pernet_ops_rwsem. Hence add the > corresponding lockdep expression to silence the following > false-positive warning at boot: Thanks for the fix, the warning has been annoying me as well! > [ 0.645292] ============================= > [ 0.645294] WARNING: suspicious RCU usage > [ 0.645296] 5.5.4-stable #17 Not tainted > [ 0.645297] ----------------------------- > [ 0.645299] net/ipv4/ipmr.c:136 RCU-list traversed in non-reader section!! please provide a fuller stack trace, it would have helped the review > Signed-off-by: Amol Grover <frextrite@gmail.com> > --- > net/ipv4/ipmr.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c > index 99c864eb6e34..950ffe9943da 100644 > --- a/net/ipv4/ipmr.c > +++ b/net/ipv4/ipmr.c > @@ -109,9 +109,10 @@ static void mroute_clean_tables(struct mr_table *mrt, int flags); > static void ipmr_expire_process(struct timer_list *t); > > #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)) Thoughts? _______________________________________________ Linux-kernel-mentees mailing list Linux-kernel-mentees@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees
next prev parent reply other threads:[~2020-05-09 21:19 UTC|newest] Thread overview: 18+ 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 ` [Linux-kernel-mentees] " 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 7:22 ` [Linux-kernel-mentees] " Amol Grover 2020-05-09 21:19 ` Jakub Kicinski [this message] 2020-05-09 21:19 ` Jakub Kicinski 2020-05-12 5:17 ` Madhuparna Bhowmik 2020-05-12 5:17 ` [Linux-kernel-mentees] " Madhuparna Bhowmik 2020-05-12 16:32 ` Jakub Kicinski 2020-05-12 16:32 ` [Linux-kernel-mentees] " Jakub Kicinski 2020-05-13 5:34 ` Madhuparna Bhowmik 2020-05-13 5:34 ` [Linux-kernel-mentees] " Madhuparna Bhowmik 2020-05-12 17:17 ` Amol Grover 2020-05-12 17:17 ` [Linux-kernel-mentees] " Amol Grover 2020-05-12 21:59 ` Jakub Kicinski 2020-05-12 21:59 ` [Linux-kernel-mentees] " Jakub Kicinski 2020-05-13 11:54 ` Stephen Rothwell 2020-05-13 11:54 ` [Linux-kernel-mentees] " Stephen Rothwell
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