Messages in this thread | | | Date | Sat, 9 May 2020 14:19:38 -0700 | From | Jakub Kicinski <> | Subject | Re: [PATCH net 2/2 RESEND] ipmr: Add lockdep expression to ipmr_for_each_table macro |
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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?
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