Messages in this thread Patch in this message |  | | Subject | Re: [PATCH v2] net: ipmr: fix suspicious RCU warning | | From | Eric Dumazet <> | | Date | Wed, 20 Nov 2019 09:45:18 -0800 |
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On 11/20/19 7:22 AM, Anders Roxell wrote: > When booting an arm64 allmodconfig kernel on linux-next next-20191115 > The following "suspicious RCU usage" warning shows up. This bug seems > to have been introduced by commit f0ad0860d01e ("ipv4: ipmr: support > multiple tables") in 2010, but the warning was added only in this past > year by commit 28875945ba98 ("rcu: Add support for consolidated-RCU > reader checking"). > > [ 32.496021][ T1] ============================= > [ 32.497616][ T1] WARNING: suspicious RCU usage > [ 32.499614][ T1] 5.4.0-rc6-next-20191108-00003-gf74bac957b5c-dirty #2 Not tainted > [ 32.502018][ T1] ----------------------------- > [ 32.503976][ T1] net/ipv4/ipmr.c:136 RCU-list traversed in non-reader section!! > [ 32.506746][ T1] > [ 32.506746][ T1] other info that might help us debug this: > [ 32.506746][ T1] > [ 32.509794][ T1] > [ 32.509794][ T1] rcu_scheduler_active = 2, debug_locks = 1 > [ 32.512661][ T1] 1 lock held by swapper/0/1: > [ 32.514169][ T1] #0: ffffa000150dd678 (pernet_ops_rwsem){+.+.}, at: register_pernet_subsys+0x24/0x50 > [ 32.517621][ T1] > [ 32.517621][ T1] stack backtrace: > [ 32.519930][ T1] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.4.0-rc6-next-20191108-00003-gf74bac957b5c-dirty #2 > [ 32.523063][ T1] Hardware name: linux,dummy-virt (DT) > [ 32.524787][ T1] Call trace: > [ 32.525946][ T1] dump_backtrace+0x0/0x2d0 > [ 32.527433][ T1] show_stack+0x20/0x30 > [ 32.528811][ T1] dump_stack+0x204/0x2ac > [ 32.530258][ T1] lockdep_rcu_suspicious+0xf4/0x108 > [ 32.531993][ T1] ipmr_get_table+0xc8/0x170 > [ 32.533496][ T1] ipmr_new_table+0x48/0xa0 > [ 32.535002][ T1] ipmr_net_init+0xe8/0x258 > [ 32.536465][ T1] ops_init+0x280/0x2d8 > [ 32.537876][ T1] register_pernet_operations+0x210/0x420 > [ 32.539707][ T1] register_pernet_subsys+0x30/0x50 > [ 32.541372][ T1] ip_mr_init+0x54/0x180 > [ 32.542785][ T1] inet_init+0x25c/0x3e8 > [ 32.544186][ T1] do_one_initcall+0x4c0/0xad8 > [ 32.545757][ T1] kernel_init_freeable+0x3e0/0x500 > [ 32.547443][ T1] kernel_init+0x14/0x1f0 > [ 32.548875][ T1] ret_from_fork+0x10/0x18 > > This commit therefore holds RTNL mutex around the problematic code path, > which is function ipmr_rules_init() in ipmr_net_init(). This commit > also adds a lockdep_rtnl_is_held() check to the ipmr_for_each_table() > macro. > > Suggested-by: David Miller <davem@davemloft.net> > Reviewed-by: Paul E. McKenney <paulmck@kernel.org> > Signed-off-by: Anders Roxell <anders.roxell@linaro.org> > --- > net/ipv4/ipmr.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c > index 6e68def66822..53dff9a0e60a 100644 > --- a/net/ipv4/ipmr.c > +++ b/net/ipv4/ipmr.c > @@ -110,7 +110,8 @@ 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) > + list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list, \ > + lockdep_rtnl_is_held()) > > static struct mr_table *ipmr_mr_table_iter(struct net *net, > struct mr_table *mrt) > @@ -3086,7 +3087,9 @@ static int __net_init ipmr_net_init(struct net *net) > if (err) > goto ipmr_notifier_fail; > > + rtnl_lock(); > err = ipmr_rules_init(net); > + rtnl_unlock(); > if (err < 0) > goto ipmr_rules_fail;
Hmmm... this might have performance impact for creation of a new netns
Since the 'struct net' is not yet fully initialized (thus published/visible), should we really have to grab RTNL (again) only to silence a warning ?
What about the following alternative ?
diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c index 6e68def66822f47fc08d94eddd32a4bd4f9fdfb0..b6dcdce08f1d82c83756a319623e24ae0174092c 100644 --- a/net/ipv4/ipmr.c +++ b/net/ipv4/ipmr.c @@ -94,7 +94,7 @@ static DEFINE_SPINLOCK(mfc_unres_lock); static struct kmem_cache *mrt_cachep __ro_after_init; -static struct mr_table *ipmr_new_table(struct net *net, u32 id); +static struct mr_table *ipmr_new_table(struct net *net, u32 id, bool init); static void ipmr_free_table(struct mr_table *mrt); static void ip_mr_forward(struct net *net, struct mr_table *mrt, @@ -245,7 +245,7 @@ static int __net_init ipmr_rules_init(struct net *net) INIT_LIST_HEAD(&net->ipv4.mr_tables); - mrt = ipmr_new_table(net, RT_TABLE_DEFAULT); + mrt = ipmr_new_table(net, RT_TABLE_DEFAULT, true); if (IS_ERR(mrt)) { err = PTR_ERR(mrt); goto err1; @@ -322,7 +322,7 @@ static int __net_init ipmr_rules_init(struct net *net) { struct mr_table *mrt; - mrt = ipmr_new_table(net, RT_TABLE_DEFAULT); + mrt = ipmr_new_table(net, RT_TABLE_DEFAULT, true); if (IS_ERR(mrt)) return PTR_ERR(mrt); net->ipv4.mrt = mrt; @@ -392,7 +392,7 @@ static struct mr_table_ops ipmr_mr_table_ops = { .cmparg_any = &ipmr_mr_table_ops_cmparg_any, }; -static struct mr_table *ipmr_new_table(struct net *net, u32 id) +static struct mr_table *ipmr_new_table(struct net *net, u32 id, bool init) { struct mr_table *mrt; @@ -400,9 +400,11 @@ static struct mr_table *ipmr_new_table(struct net *net, u32 id) if (id != RT_TABLE_DEFAULT && id >= 1000000000) return ERR_PTR(-EINVAL); - mrt = ipmr_get_table(net, id); - if (mrt) - return mrt; + if (!init) { + mrt = ipmr_get_table(net, id); + if (mrt) + return mrt; + } return mr_table_alloc(net, id, &ipmr_mr_table_ops, ipmr_expire_process, ipmr_new_table_set); @@ -1547,7 +1549,7 @@ int ip_mroute_setsockopt(struct sock *sk, int optname, char __user *optval, if (sk == rtnl_dereference(mrt->mroute_sk)) { ret = -EBUSY; } else { - mrt = ipmr_new_table(net, uval); + mrt = ipmr_new_table(net, uval, false); if (IS_ERR(mrt)) ret = PTR_ERR(mrt); else
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