Re: [PATCH v2] net: ipmr: fix suspicious RCU warning

From: Anders Roxell
Date: Thu Nov 21 2019 - 05:17:53 EST

On Thu, 21 Nov 2019 at 08:15, Anders Roxell <anders.roxell@xxxxxxxxxx> wrote:
>
> On Wed, 20 Nov 2019 at 18:45, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:
> >
> >
> >
> > On 11/20/19 7:22 AM, Anders Roxell wrote:

[snippet]

> > > + 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 ?
>
> I tried what you suggested, unfortunately, I still got the warning.

I was wrong, so if I also add "lockdep_rtnl_is_held()" to the
"ipmr_for_each_table()" macro it works.

>
>
> [ 43.253850][ T1] =============================
> [ 43.255473][ T1] WARNING: suspicious RCU usage
> [ 43.259068][ T1]
> 5.4.0-rc8-next-20191120-00003-g3aa7c2a8649e-dirty #6 Not tainted
> [ 43.263078][ T1] -----------------------------
> [ 43.265134][ T1] net/ipv4/ipmr.c:1759 RCU-list traversed in
> non-reader section!!
> [ 43.267587][ T1]
> [ 43.267587][ T1] other info that might help us debug this:
> [ 43.267587][ T1]
> [ 43.271129][ T1]
> [ 43.271129][ T1] rcu_scheduler_active = 2, debug_locks = 1
> [ 43.274021][ T1] 2 locks held by swapper/0/1:
> [ 43.275532][ T1] #0: ffff000065abeaa0 (&dev->mutex){....}, at:
> __device_driver_lock+0xa0/0xb0
> [ 43.278930][ T1] #1: ffffa000153017f0 (rtnl_mutex){+.+.}, at:
> rtnl_lock+0x1c/0x28
> [ 43.282023][ T1]
> [ 43.282023][ T1] stack backtrace:
> [ 43.283921][ T1] CPU: 0 PID: 1 Comm: swapper/0 Not tainted
> 5.4.0-rc8-next-20191120-00003-g3aa7c2a8649e-dirty #6
> [ 43.287152][ T1] Hardware name: linux,dummy-virt (DT)
> [ 43.288920][ T1] Call trace:
> [ 43.290057][ T1] dump_backtrace+0x0/0x2d0
> [ 43.291535][ T1] show_stack+0x20/0x30
> [ 43.292967][ T1] dump_stack+0x204/0x2ac
> [ 43.294423][ T1] lockdep_rcu_suspicious+0xf4/0x108
> [ 43.296163][ T1] ipmr_device_event+0x100/0x1e8
> [ 43.297812][ T1] notifier_call_chain+0x100/0x1a8
> [ 43.299486][ T1] raw_notifier_call_chain+0x38/0x48
> [ 43.301248][ T1] call_netdevice_notifiers_info+0x128/0x148
> [ 43.303158][ T1] rollback_registered_many+0x684/0xb48
> [ 43.304963][ T1] rollback_registered+0xd8/0x150
> [ 43.306595][ T1] unregister_netdevice_queue+0x194/0x1b8
> [ 43.308406][ T1] unregister_netdev+0x24/0x38
> [ 43.310012][ T1] virtnet_remove+0x44/0x78
> [ 43.311519][ T1] virtio_dev_remove+0x5c/0xc0
> [ 43.313114][ T1] really_probe+0x508/0x920
> [ 43.314635][ T1] driver_probe_device+0x164/0x230
> [ 43.316337][ T1] device_driver_attach+0x8c/0xc0
> [ 43.318024][ T1] __driver_attach+0x1e0/0x1f8
> [ 43.319584][ T1] bus_for_each_dev+0xf0/0x188
> [ 43.321169][ T1] driver_attach+0x34/0x40
> [ 43.322645][ T1] bus_add_driver+0x204/0x3c8
> [ 43.324202][ T1] driver_register+0x160/0x1f8
> [ 43.325788][ T1] register_virtio_driver+0x7c/0x88
> [ 43.327480][ T1] virtio_net_driver_init+0xa8/0xf4
> [ 43.329196][ T1] do_one_initcall+0x4c0/0xad8
> [ 43.330767][ T1] kernel_init_freeable+0x3e0/0x500
> [ 43.332444][ T1] kernel_init+0x14/0x1f0
> [ 43.333901][ T1] ret_from_fork+0x10/0x18
>
>
> Cheers,
> Anders
>
> >
> > 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,
@@ -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)


Cheers,
Anders

> > 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
> >
> >