On Tue, May 12, 2020 at 10:47:05AM +0530, Madhuparna Bhowmik wrote: > 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 <frextr...@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)) > >
Jakub, I agree, this condition looks better (and correct) than the one I proposed. I'll do the changes as necessary. Also, do you want me to add the full trace to the git commit body as well? I omitted it on purpose to not make it messy. > (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 > Thank you for the stacktrace Madhuparna. > 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