This reverts commit 8d7e5dee.

To protect netns id, the nsid_lock is used when netns id is being
allocated and removed by peernet2id_alloc() and unhash_nsid().
The nsid_lock can be used in BH context but only spin_lock() is used
in this code.
Using spin_lock() instead of spin_lock_bh() can result in a deadlock in
the following scenario reported by the lockdep.
In order to avoid a deadlock, the spin_lock_bh() should be used instead
of spin_lock() to acquire nsid_lock.

Test commands:
    ip netns del nst
    ip netns add nst
    ip link add veth1 type veth peer name veth2
    ip link set veth1 netns nst
    ip netns exec nst ip link add name br1 type bridge vlan_filtering 1
    ip netns exec nst ip link set dev br1 up
    ip netns exec nst ip link set dev veth1 master br1
    ip netns exec nst ip link set dev veth1 up
    ip netns exec nst ip link add macvlan0 link br1 up type macvlan

Splat looks like:
[   33.615860][  T607] WARNING: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected
[   33.617194][  T607] 5.9.0-rc1+ #665 Not tainted
[ ... ]
[   33.670615][  T607] Chain exists of:
[   33.670615][  T607]   &mc->mca_lock --> &bridge_netdev_addr_lock_key --> &net->nsid_lock
[   33.670615][  T607]
[   33.673118][  T607]  Possible interrupt unsafe locking scenario:
[   33.673118][  T607]
[   33.674599][  T607]        CPU0                    CPU1
[   33.675557][  T607]        ----                    ----
[   33.676516][  T607]   lock(&net->nsid_lock);
[   33.677306][  T607]                                local_irq_disable();
[   33.678517][  T607]                                lock(&mc->mca_lock);
[   33.679725][  T607]                                lock(&bridge_netdev_addr_lock_key);
[   33.681166][  T607]   <Interrupt>
[   33.681791][  T607]     lock(&mc->mca_lock);
[   33.682579][  T607]
[   33.682579][  T607]  *** DEADLOCK ***
[ ... ]
[   33.922046][  T607] stack backtrace:
[   33.922999][  T607] CPU: 3 PID: 607 Comm: ip Not tainted 5.9.0-rc1+ #665
[   33.924099][  T607] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014
[   33.925714][  T607] Call Trace:
[   33.926238][  T607]  dump_stack+0x78/0xab
[   33.926905][  T607]  check_irq_usage+0x70b/0x720
[   33.927708][  T607]  ? iterate_chain_key+0x60/0x60
[   33.928507][  T607]  ? check_path+0x22/0x40
[   33.929201][  T607]  ? check_noncircular+0xcf/0x180
[   33.930024][  T607]  ? __lock_acquire+0x1952/0x1f20
[   33.930860][  T607]  __lock_acquire+0x1952/0x1f20
[   33.931667][  T607]  lock_acquire+0xaf/0x3a0
[   33.932366][  T607]  ? peernet2id_alloc+0x3a/0x170
[   33.933147][  T607]  ? br_port_fill_attrs+0x54c/0x6b0 [bridge]
[   33.934140][  T607]  ? br_port_fill_attrs+0x5de/0x6b0 [bridge]
[   33.935113][  T607]  ? kvm_sched_clock_read+0x14/0x30
[   33.935974][  T607]  _raw_spin_lock+0x30/0x70
[   33.936728][  T607]  ? peernet2id_alloc+0x3a/0x170
[   33.937523][  T607]  peernet2id_alloc+0x3a/0x170
[   33.938313][  T607]  rtnl_fill_ifinfo+0xb5e/0x1400
[   33.939091][  T607]  rtmsg_ifinfo_build_skb+0x8a/0xf0
[   33.939953][  T607]  rtmsg_ifinfo_event.part.39+0x17/0x50
[   33.940863][  T607]  rtmsg_ifinfo+0x1f/0x30
[   33.941571][  T607]  __dev_notify_flags+0xa5/0xf0
[   33.942376][  T607]  ? __irq_work_queue_local+0x49/0x50
[   33.943249][  T607]  ? irq_work_queue+0x1d/0x30
[   33.943993][  T607]  ? __dev_set_promiscuity+0x7b/0x1a0
[   33.944878][  T607]  __dev_set_promiscuity+0x7b/0x1a0
[   33.945758][  T607]  dev_set_promiscuity+0x1e/0x50
[   33.946582][  T607]  br_port_set_promisc+0x1f/0x40 [bridge]
[   33.947487][  T607]  br_manage_promisc+0x8b/0xe0 [bridge]
[   33.948388][  T607]  __dev_set_promiscuity+0x123/0x1a0
[   33.949244][  T607]  __dev_set_rx_mode+0x68/0x90
[   33.950021][  T607]  dev_uc_add+0x50/0x60
[   33.950720][  T607]  macvlan_open+0x18e/0x1f0 [macvlan]
[   33.951601][  T607]  __dev_open+0xd6/0x170
[   33.952269][  T607]  __dev_change_flags+0x181/0x1d0
[   33.953056][  T607]  rtnl_configure_link+0x2f/0xa0
[   33.953884][  T607]  __rtnl_newlink+0x6b9/0x8e0
[   33.954665][  T607]  ? __lock_acquire+0x95d/0x1f20
[   33.955450][  T607]  ? lock_acquire+0xaf/0x3a0
[   33.956193][  T607]  ? is_bpf_text_address+0x5/0xe0
[   33.956999][  T607]  rtnl_newlink+0x47/0x70
Acked-by: Guillaume Nault <gnault@redhat.com>
Fixes: 8d7e5dee ("netns: don't disable BHs when locking "nsid_lock"")
Reported-by: syzbot+3f960c64a104eaa2c813@syzkaller.appspotmail.com
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>