Messages in this thread | | | From | Madhuparna Bhowmik <> | Date | Tue, 12 May 2020 10:47:05 +0530 | Subject | Re: [PATCH net 2/2 RESEND] ipmr: Add lockdep expression to ipmr_for_each_table macro |
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On Sat, May 09, 2020 at 02:19:38PM -0700, Jakub Kicinski wrote: > 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)) > (adding Stephen)
Hi Jakub,
Thank you for your suggestion about this patch. Here is a stack trace for ipmr.c:
[ 1.515015] TCP: Hash tables configured (established 8192 bind 8192) [ 1.516790] UDP hash table entries: 512 (order: 3, 49152 bytes, linear) [ 1.518177] UDP-Lite hash table entries: 512 (order: 3, 49152 bytes, linear) [ 1.519805] [ 1.520178] ============================= [ 1.520982] WARNING: suspicious RCU usage [ 1.521798] 5.7.0-rc2-00006-gb35af6a26b7c6f #1 Not tainted [ 1.522910] ----------------------------- [ 1.523671] net/ipv4/ipmr.c:136 RCU-list traversed in non-reader section!! [ 1.525218] [ 1.525218] other info that might help us debug this: [ 1.525218] [ 1.526731] [ 1.526731] rcu_scheduler_active = 2, debug_locks = 1 [ 1.528004] 1 lock held by swapper/1: [ 1.528714] #0: c20be1d8 (pernet_ops_rwsem){+.+.}-{3:3}, at: register_pernet_subsys+0xd/0x30 [ 1.530433] [ 1.530433] stack backtrace: [ 1.531262] CPU: 0 PID: 1 Comm: swapper Not tainted 5.7.0-rc2-00006-gb35af6a26b7c6f #1 [ 1.532729] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014 [ 1.534305] Call Trace: [ 1.534758] ? ipmr_get_table+0x3c/0x70 [ 1.535430] ? ipmr_new_table+0x1c/0x60 [ 1.536173] ? ipmr_net_init+0x7b/0x170 [ 1.536923] ? register_pernet_subsys+0xd/0x30 [ 1.537810] ? ops_init+0x1a0/0x1e0 [ 1.538518] ? kmem_cache_create_usercopy+0x28a/0x350 [ 1.539752] ? register_pernet_operations+0xc9/0x1c0 [ 1.540630] ? ipv4_offload_init+0x65/0x65 [ 1.541451] ? register_pernet_subsys+0x19/0x30 [ 1.542357] ? ip_mr_init+0x28/0xff [ 1.543079] ? inet_init+0x17b/0x249 [ 1.543773] ? do_one_initcall+0xc5/0x240 [ 1.544532] ? parse_args+0x192/0x350 [ 1.545266] ? rcu_read_lock_sched_held+0x2f/0x60 [ 1.546180] ? trace_initcall_level+0x61/0x93 [ 1.547061] ? kernel_init_freeable+0x112/0x18a [ 1.547978] ? kernel_init_freeable+0x12b/0x18a [ 1.548974] ? rest_init+0x220/0x220 [ 1.549792] ? kernel_init+0x8/0x100 [ 1.550548] ? rest_init+0x220/0x220 [ 1.551288] ? schedule_tail_wrapper+0x6/0x8 [ 1.552136] ? rest_init+0x220/0x220 [ 1.552873] ? ret_from_fork+0x2e/0x38
ALso, there is a similar warning for ip6mr.c :
============================= WARNING: suspicious RCU usage 5.7.0-rc4-next-20200507-syzkaller #0 Not tainted ----------------------------- net/ipv6/ip6mr.c:124 RCU-list traversed in non-reader section!!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1 1 lock held by swapper/0/1: #0: ffffffff8a7aae30 (pernet_ops_rwsem){+.+.}-{3:3}, at: register_pernet_subsys+0x16/0x40 net/core/net_namespace.c:1257
stack backtrace: CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.7.0-rc4-next-20200507-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x18f/0x20d lib/dump_stack.c:118 ip6mr_get_table+0x153/0x180 net/ipv6/ip6mr.c:124 ip6mr_new_table+0x1b/0x70 net/ipv6/ip6mr.c:382 ip6mr_rules_init net/ipv6/ip6mr.c:236 [inline] ip6mr_net_init+0x133/0x3f0 net/ipv6/ip6mr.c:1310 ops_init+0xaf/0x420 net/core/net_namespace.c:151 __register_pernet_operations net/core/net_namespace.c:1140 [inline] register_pernet_operations+0x346/0x840 net/core/net_namespace.c:1217 register_pernet_subsys+0x25/0x40 net/core/net_namespace.c:1258 ip6_mr_init+0x49/0x152 net/ipv6/ip6mr.c:1363 inet6_init+0x1d7/0x6dc net/ipv6/af_inet6.c:1037 do_one_initcall+0x10a/0x7d0 init/main.c:1159 do_initcall_level init/main.c:1232 [inline] do_initcalls init/main.c:1248 [inline] do_basic_setup init/main.c:1268 [inline] kernel_init_freeable+0x501/0x5ae init/main.c:1454 kernel_init+0xd/0x1bb init/main.c:1359 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:351 Segment Routing with IPv6 mip6: Mobile IPv6 sit: IPv6, IPv4 and MPLS over IPv4 tunneling driver ip6_gre: GRE over IPv6 tunneling driver
> Thoughts?
Do you think a similar fix (the one you suggested) is also applicable in the ip6mr case.
Thank you, Madhuparna
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