Re: [PATCH v3] lockdep: Allow tuning tracing capacity constants.

From: Tetsuo Handa
Date: Thu Dec 03 2020 - 08:47:57 EST

On Sun, Nov 22, 2020 at 2:56 AM Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote:
> Peter, you guessed that the culprit is sysfs at
> https://lkml.kernel.org/r/20200916115057.GO2674@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx , but
> syzbot reported at https://syzkaller.appspot.com/text?tag=MachineInfo&x=99b8f2b092d9714f
> that "BUG: MAX_LOCKDEP_ENTRIES too low!" can occur on a VM with only 2 CPUs.
> Is your guess catching the culprit?
>
> We could improve a few locks, but as a whole we won't be able to afford keeping
> sum of individual dependencies under current threshold. Therefore, allow lockdep to
> tune the capacity and allow syzkaller to dump when reaching the capacity will be
> the way to go.

An example dump from a VM with only 2 CPUs
( https://syzkaller.appspot.com/text?tag=CrashLog&x=12016d55500000 ) had
a chain with more than kn->active#number 150 entries.

kn->active#number is initialized by __kernfs_create_file() but it is not
deinitialized (there is no method for erasing lockdep map?) by kernfs_put().
Since syzkaller continues object creation/deletion via fuzz testing until
kernel crashes, __kernfs_create_file() are called for so many times?



struct kernfs_node *__kernfs_create_file(struct kernfs_node *parent,
const char *name,
umode_t mode, kuid_t uid, kgid_t gid,
loff_t size,
const struct kernfs_ops *ops,
void *priv, const void *ns,
struct lock_class_key *key)
{
(...snipped...)
kn = kernfs_new_node(parent, name, (mode & S_IALLUGO) | S_IFREG,
uid, gid, flags);
if (!kn)
return ERR_PTR(-ENOMEM);

kn->attr.ops = ops;
kn->attr.size = size;
kn->ns = ns;
kn->priv = priv;

#ifdef CONFIG_DEBUG_LOCK_ALLOC
if (key) {
lockdep_init_map(&kn->dep_map, "kn->active", key, 0);
kn->flags |= KERNFS_LOCKDEP;
}
#endif
(...snipped...)
}

void kernfs_put(struct kernfs_node *kn)
{
(...snipped...)
kmem_cache_free(kernfs_node_cache, kn);
(...snipped...)
}



FD: 919 BD: 59 +.+.: rtnl_mutex
->fs_reclaim
->depot_lock
->pcpu_alloc_mutex
->&x->wait#6
->&obj_hash[i].lock
->gdp_mutex
->&k->list_lock
->lock#2
->kernfs_mutex
->bus_type_sem
->sysfs_symlink_target_lock
->&____s->seqcount
->&dev->power.lock
->dpm_list_mtx
->uevent_sock_mutex
->&zone->lock
->running_helpers_waitq.lock
->subsys mutex#17
->dev_hotplug_mutex
->dev_base_lock
->input_pool.lock
->nl_table_lock
->nl_table_wait.lock
->net_rwsem
->&tbl->lock
->sysctl_lock
->&rq->lock
->krc.lock
->cpu_hotplug_lock
->kthread_create_lock
->&p->pi_lock
->&cfs_rq->removed.lock
->&x->wait
->&p->alloc_lock
->&cpuset_rwsem
->wq_pool_mutex
->&crng->lock
->rcu_node_0
->&rcu_state.expedited_wq
->&n->list_lock
->&pool->lock
->pool_lock
->lweventlist_lock
->rtnl_mutex.wait_lock
->proc_subdir_lock
->proc_inum_ida.xa_lock
->&k->k_lock
->pcpu_lock
->param_lock
->logbuf_lock
->(console_sem).lock
->subsys mutex#52
->pin_fs_lock
->&sb->s_type->i_mutex_key#3
->&local->iflist_mtx
->&wdev->mtx
->subsys mutex#53
->&sdata->sec_mtx
->&local->iflist_mtx#2
->lock#6
->net_dm_mutex
->failover_lock
->&tn->lock
->&cn->lock
->&ndev->lock
->&idev->mc_lock
->&mc->mca_lock
->&base->lock
->j1939_netdev_lock
->&pnettable->lock
->&vn->sock_lock
->&reg_requests_lock
->&reg_pending_beacons_lock
->&reg_indoor_lock
->_xmit_LOOPBACK
->(inetaddr_validator_chain).rwsem
->(inetaddr_chain).rwsem
->&in_dev->mc_tomb_lock
->&im->lock
->fib_info_lock
->cbs_list_lock
->taprio_list_lock
->(inet6addr_validator_chain).rwsem
->addrconf_hash_lock
->&ifa->lock
->&tb->tb6_lock
->rlock-AF_NETLINK
->_xmit_ETHER
->noop_qdisc.q.lock
->quarantine_lock
->kernfs_mutex.wait_lock
->x25_neigh_list_lock
->&mm->mmap_lock#2
->free_vmap_area_lock
->vmap_area_lock
->&ul->lock
->&n->lock
->&pn->hash_lock
->init_mm.page_table_lock
->&nr_netdev_addr_lock_key
->listen_lock
->&r->consumer_lock
->batched_entropy_u32.lock
->(switchdev_blocking_notif_chain).rwsem
->&br->hash_lock
->nf_hook_mutex
->console_owner_lock
->console_owner
->&bat_priv->tvlv.handler_list_lock
->&bat_priv->tvlv.container_list_lock
->&bat_priv->softif_vlan_list_lock
->key#14
->&bat_priv->tt.changes_list_lock
->tk_core.seq.seqcount
->&wq->mutex
->init_lock
->deferred_lock
->target_list_lock
->&br->lock
->&dev_addr_list_lock_key/1
->team->team_lock_key
->&hard_iface->bat_iv.ogm_buff_mutex
->ptype_lock
->&hsr->list_lock
->&rnp->exp_wq[1]
->&rnp->exp_wq[2]
->&rnp->exp_wq[3]
->&xa->xa_lock#7
->&dev_addr_list_lock_key#3/1
->req_lock
->&x->wait#9
->subsys mutex#74
->&devlink_port->type_lock
->pgd_lock
->&dev->tx_global_lock
->&rnp->exp_wq[0]
->&sch->q.lock
->(&tbl->proxy_timer)
->class
->bpf_devs_lock
->devnet_rename_sem
->&net->nft.commit_mutex
->&ent->pde_unload_lock
->team->team_lock_key#2
->&wg->device_update_lock
->_xmit_SIT
->&bridge_netdev_addr_lock_key/1
->team->team_lock_key#3
->_xmit_NONE
->_xmit_TUNNEL
->_xmit_IPGRE
->mount_lock
->team->team_lock_key#4
->_xmit_TUNNEL6
->team->team_lock_key#5
->&dev_addr_list_lock_key#2/1
->team->team_lock_key#6
->_xmit_ETHER/1
->&nn->netlink_tap_lock
->&batadv_netdev_addr_lock_key/1
->&vlan_netdev_addr_lock_key/1
->&macvlan_netdev_addr_lock_key/1
->&br->multicast_lock
->&macsec_netdev_addr_lock_key/1
->key#18
->&bat_priv->tt.commit_lock
->&sb->s_type->i_lock_key#8
->k-slock-AF_INET/1
->k-slock-AF_INET#2
->k-sk_lock-AF_INET
->k-slock-AF_INET6
->k-sk_lock-AF_INET6
->&ul->lock#2
->&____s->seqcount#5
->&nf_conntrack_locks[i]
->&wdev->event_lock
->&wdev->mgmt_registrations_lock
->&local->key_mtx
->&dentry->d_lock
->&sb->s_type->i_lock_key#7
->&s->s_inode_list_lock
->&xa->xa_lock#4
->&rfkill->lock
->&local->chanctx_mtx
->&data->mutex
->&local->queue_stop_reason_lock
->&sch->seqlock
->&cpuctx_lock
->act_mod_lock
->&tn->idrinfo->lock
->vmap_purge_lock
->cpa_lock
->&fp->aux->used_maps_mutex
->&p->tcfa_lock
->slock-AF_INET6
->sk_lock-AF_INET6
->__ip_vs_mutex
->flowtable_lock
->&net->xdp.lock
->mirred_list_lock
->&pnn->pndevs.lock
->&pnn->routes.lock
->kn->active#164
->kn->active#165
->kernfs_idr_lock
->kn->active#166
->kn->active#167
->kn->active#168
->kn->active#169
->kn->active#170
->kn->active#171
->kn->active#172
->kn->active#173
->kn->active#174
->kn->active#175
->dev_pm_qos_sysfs_mtx
->kn->active#80
->kn->active#81
->kn->active#82
->kn->active#83
->kn->active#84
->kn->active#2
->kn->active#176
->kn->active#177
->kn->active#178
->kn->active#179
->kn->active#180
->kn->active#181
->kn->active#182
->kn->active#183
->kn->active#184
->kn->active#185
->kn->active#186
->kn->active#187
->kn->active#188
->kn->active#189
->kn->active#190
->kn->active#191
->kn->active#192
->kn->active#193
->kn->active#194
->kn->active#195
->kn->active#196
->kn->active#197
->kn->active#198
->kn->active#199
->kn->active#200
->kn->active#53
->kn->active#201
->kn->active#64
->kn->active#63
->kn->active#62
->kn->active#55
->kn->active#56
->kn->active#202
->kn->active#203
->kn->active#54
->kn->active#204
->kn->active#205
->kn->active#206
->kn->active#207
->kn->active#208
->kn->active#209
->kn->active#210
->kn->active#211
->kn->active#212
->kn->active#213
->kn->active#214
->kn->active#215
->kn->active#216
->kn->active#217
->kn->active#218
->kn->active#65
->kn->active#219
->kn->active#220
->kn->active#221
->kn->active#222
->deferred_probe_mutex
->wfs_lock
->device_links_lock
->qdisc_mod_lock
->dev->qdisc_running_key ?: &qdisc_running_key
->(&q->adapt_timer)
->&block->lock
->&block->cb_lock
->(&q->adapt_timer)#2
->&chain->filter_chain_lock
->cls_mod_lock
->&head->masks_lock
->&tp->lock
->&tn->idrinfo->lock#2
->&block->proto_destroy_lock
->lock#10
->&tun->lock
->wlock-AF_UNSPEC
->elock-AF_UNSPEC
->kn->active#343
->kn->active#344
->kn->active#345
->pcpu_alloc_mutex.wait_lock
->rcu_state.exp_mutex.wait_lock
->&rnp->exp_lock
->(&fnew->perturb_timer)
->ematch_mod_lock
->&pn->all_ppp_mutex
->&ppp->rlock
->&ppp->wlock
->&dev_addr_list_lock_key#4
->&pf->rwait
->&macvlan_netdev_addr_lock_key/2
->kn->active#71
->&dev->devres_lock
->kn->active#346
->kn->active#347
->kn->active#348
->kn->active#349
->rcu_state.exp_mutex
->&tn->idrinfo->lock#3
->netdev_unregistering_wq.lock
->&(&net->nexthop.notifier_chain)->rwsem
->&caifn->caifdevs.lock
->&net->rules_mod_lock
->(&mrt->ipmr_expire_timer)
->&ht->mutex
->nf_connlabels_lock
->&tn->idrinfo->lock#4
->zones_mutex
->uevent_sock_mutex.wait_lock
->napi_hash_lock
->kn->active#356
->kn->active#357
->kn->active#358
->kn->active#359
->kn->active#360
->kn->active#361
->kn->active#362
->kn->active#363
->kn->active#364
->kn->active#365
->kn->active#366
->kn->active#367
->kn->active#368
->kn->active#369
->kn->active#370
->kn->active#371
->kn->active#372
->kn->active#373
->kn->active#374
->kn->active#375
->kn->active#376
->kn->active#377
->kn->active#378
->kn->active#379
->kn->active#380
->kn->active#381
->kn->active#382
->kn->active#383
->kn->active#384
->kn->active#385
->kn->active#386
->kn->active#387
->kn->active#388
->kn->active#389
->kn->active#390
->kn->active#391
->kn->active#392
->kn->active#393
->kn->active#394
->kn->active#395
->kn->active#396
->kn->active#397
->kn->active#398
->kn->active#399
->kn->active#400
->kn->active#401
->&bridge_netdev_addr_lock_key
->rcu_state.barrier_mutex
->&app->lock#2
->(&app->join_timer)#2
->(&app->periodic_timer)
->&list->lock#13
->(&app->join_timer)
->&app->lock
->&list->lock#12
->&tn->idrinfo->lock#5
->ife_mod_lock
->_xmit_NETROM#2
->&this->info_list_lock
->&local->mtx
->&lock->wait_lock
->&list->lock#2
->(&port->multicast_router_timer)
->kn->active#404
->kn->active#405
->kn->active#406
->kn->active#407
->kn->active#408
->kn->active#409
->kn->active#410
->kn->active#411
->kn->active#412
->kn->active#413
->kn->active#414
->kn->active#415
->kn->active#416
->kn->active#417
->kn->active#418
->kn->active#419
->kn->active#420
->kn->active#421
->kn->active#422
->kn->active#423
->kn->active#424
->kn->active#425
->kn->active#426
->kn->active#427
->kn->active#428
->kn->active#429
->kn->active#430
->kn->active#431
->kn->active#432
->kn->active#433
->kn->active#434
->&tn->idrinfo->lock#6
->&local->sta_mtx
->acaddr_hash_lock
->(&br->hello_timer)
->(&br->topology_change_timer)
->(&br->tcn_timer)
->(&br->multicast_router_timer)
->(&br->ip4_other_query.timer)
->(&br->ip4_own_query.timer)
->(&br->ip6_other_query.timer)
->(&br->ip6_own_query.timer)
->slock-AF_CAN
->sk_lock-AF_CAN
->&list->lock#16
->&wg->socket_update_lock
->&table->hash[i].lock
->k-clock-AF_INET
->k-clock-AF_INET6
->&mc_lst->sflock
->&tn->idrinfo->lock#7
->_xmit_AX25
->&bridge_netdev_addr_lock_key/2
->fastmap_lock