While running hostapd tests, the following deadlock showed up:
cfg80211_mgmt_registrations_update_wk locks the rtnl lock, which
is already hold by nl80211 when going into __cfg80211_unregister_wdev,
which flushes cfg80211_mgmt_registrations_update_wk.
[ 22.500591] ======================================================
[ 22.501296] WARNING: possible circular locking dependency detected
[ 22.501992] 5.7.0-rc7-wt #2 Not tainted
[ 22.502413] ------------------------------------------------------
[ 22.503084] wpa_supplicant/797 is trying to acquire lock:
[ 22.503680] ffff88800b29a9f8
((work_completion)(&wdev->mgmt_registrations_update_wk)){+.+.}-{0:0},
at: __flush_work+0x78/0xf0
[ 22.504903]
but task is already holding lock:
[ 22.506668] ffffffff81e954f0 (rtnl_mutex){+.+.}-{3:3}, at:
nl80211_pre_doit+0xd7/0x1a0
[ 22.507540]
which lock already depends on the new lock.
[ 22.508439]
the existing dependency chain (in reverse order) is:
[ 22.509333]
-> #1 (rtnl_mutex){+.+.}-{3:3}:
[ 22.509960] __lock_acquire+0x3a1/0x6b0
[ 22.510445] lock_acquire+0xc3/0x420
[ 22.510902] __mutex_lock+0x85/0x820
[ 22.511356] cfg80211_mgmt_registrations_update_wk+0xe/0x20
[ 22.512034] process_one_work+0x261/0x5b0
[ 22.512530] worker_thread+0x4e/0x310
[ 22.512991] kthread+0x13d/0x160
[ 22.513407] ret_from_fork+0x27/0x50
[ 22.513859]
-> #0
((work_completion)(&wdev->mgmt_registrations_update_wk)){+.+.}-{0:0}:
[ 22.514893] check_prev_add+0x8e/0x9a0
[ 22.515374] validate_chain+0x441/0x700
[ 22.515856] __lock_acquire+0x3a1/0x6b0
[ 22.519193] lock_acquire+0xc3/0x420
[ 22.524218] __flush_work+0x98/0xf0
[ 22.524664] __cfg80211_unregister_wdev+0x9b/0x150
[ 22.525260] cfg80211_netdev_notifier_call+0x3a4/0x4ef
[ 22.525874] notifier_call_chain+0x46/0xb0
[ 22.526657] rollback_registered_many+0x275/0x4e0
[ 22.528048] unregister_netdevice_queue+0xcf/0x180
[ 22.529184] ieee80211_del_iface+0xe/0x20
[ 22.529687] nl80211_del_interface+0x64/0x150
[ 22.532320] genl_family_rcv_msg+0x189/0x3b0
[ 22.533144] genl_rcv_msg+0x47/0x90
[ 22.533807] netlink_rcv_skb+0x47/0x110
[ 22.534474] genl_rcv+0x24/0x40
[ 22.535145] netlink_unicast+0x191/0x250
[ 22.536285] netlink_sendmsg+0x207/0x420
[ 22.539059] ____sys_sendmsg+0x206/0x230
[ 22.539948] ___sys_sendmsg+0xab/0xf0
[ 22.544879] __sys_sendmsg+0x51/0x90
[ 22.547945] do_syscall_64+0x4f/0x260
[ 22.548412] entry_SYSCALL_64_after_hwframe+0x49/0xb3
[ 22.549030]
other info that might help us debug this:
[ 22.549909] Possible unsafe locking scenario:
[ 22.550561] CPU0 CPU1
[ 22.551061] ---- ----
[ 22.555277] lock(rtnl_mutex);
[ 22.555631]
lock((work_completion)(&wdev->mgmt_registrations_update_wk));
[ 22.557354] lock(rtnl_mutex);
[ 22.558108]
lock((work_completion)(&wdev->mgmt_registrations_update_wk));
[ 22.559149]
*** DEADLOCK ***
[ 22.560215] 2 locks held by wpa_supplicant/797:
[ 22.560713] #0: ffffffff81e9d8d8 (cb_lock){++++}-{3:3}, at:
genl_rcv+0x15/0x40
[ 22.561513] #1: ffffffff81e954f0 (rtnl_mutex){+.+.}-{3:3}, at:
nl80211_pre_doit+0xd7/0x1a0
[ 22.562427]
stack backtrace:
[ 22.562909] CPU: 2 PID: 797 Comm: wpa_supplicant Not tainted
5.7.0-rc7-wt #2
[ 22.563673] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS ?-20200516_175120-felixonmars2 04/01/2014
[ 22.564779] Call Trace:
[ 22.565057] dump_stack+0x71/0xa0
[ 22.565434] check_noncircular+0x182/0x1a0
[ 22.565889] check_prev_add+0x8e/0x9a0
[ 22.566558] ? add_chain_cache+0x21d/0x460
[ 22.567013] validate_chain+0x441/0x700
[ 22.567441] __lock_acquire+0x3a1/0x6b0
[ 22.567869] lock_acquire+0xc3/0x420
[ 22.568296] ? __flush_work+0x78/0xf0
[ 22.568884] ? __lock_acquire+0x3c0/0x6b0
[ 22.569329] __flush_work+0x98/0xf0
[ 22.571083] ? __flush_work+0x78/0xf0
[ 22.571495] ? kvm_sched_clock_read+0x14/0x40
[ 22.572112] ? sched_clock+0x5/0x10
[ 22.572508] ? sched_clock_cpu+0xe/0xd0
[ 22.572939] ? __lock_release+0x1b0/0x2c0
[ 22.573386] ? rcu_read_lock_sched_held+0x57/0x90
[ 22.573917] ? cfg80211_mgmt_registrations_update+0x3c3/0x400
[ 22.574550] __cfg80211_unregister_wdev+0x9b/0x150
[ 22.575081] cfg80211_netdev_notifier_call+0x3a4/0x4ef
[ 22.575734] ? kvm_sched_clock_read+0x14/0x40
[ 22.576209] ? sched_clock+0x5/0x10
[ 22.576603] ? sched_clock_cpu+0xe/0xd0
[ 22.577023] ? mark_held_locks+0x45/0x70
[ 22.577454] ? __local_bh_enable_ip+0x79/0xf0
[ 22.577934] ? __trace_hardirqs_on_caller+0x62/0x90
[ 22.578514] ? rt_flush_dev+0x9d/0xb0
[ 22.578935] ? lockdep_hardirqs_on+0x7f/0x130
[ 22.579411] ? __local_bh_enable_ip+0x79/0xf0
[ 22.579886] ? cpumask_next+0x16/0x20
[ 22.580290] ? rt_flush_dev+0x2a/0xb0
[ 22.580701] notifier_call_chain+0x46/0xb0
[ 22.581152] rollback_registered_many+0x275/0x4e0
[ 22.581667] unregister_netdevice_queue+0xcf/0x180
[ 22.582197] ieee80211_del_iface+0xe/0x20
[ 22.582761] nl80211_del_interface+0x64/0x150
[ 22.583241] genl_family_rcv_msg+0x189/0x3b0
[ 22.583718] ? __lock_acquire+0x3c0/0x6b0
[ 22.584163] genl_rcv_msg+0x47/0x90
[ 22.584552] ? __lock_acquired+0xf4/0x320
[ 22.584998] ? genl_family_rcv_msg+0x3b0/0x3b0
[ 22.585512] netlink_rcv_skb+0x47/0x110
[ 22.585931] genl_rcv+0x24/0x40
[ 22.586253] netlink_unicast+0x191/0x250
[ 22.586689] netlink_sendmsg+0x207/0x420
[ 22.587117] ? __might_fault+0x3e/0x90
[ 22.587537] ? netlink_broadcast_filtered+0x1a0/0x1a0
[ 22.588091] ____sys_sendmsg+0x206/0x230
[ 22.588587] ? import_iovec+0x37/0xf0
[ 22.588991] ___sys_sendmsg+0xab/0xf0
[ 22.589397] ? __lock_acquire+0x3c0/0x6b0
[ 22.589845] ? kvm_sched_clock_read+0x14/0x40
[ 22.590313] ? sched_clock+0x5/0x10
[ 22.590698] ? sched_clock_cpu+0xe/0xd0
[ 22.591804] ? __lock_release+0x1b0/0x2c0
[ 22.592363] __sys_sendmsg+0x51/0x90
[ 22.592730] ? lockdep_hardirqs_off+0x79/0xd0
[ 22.593113] do_syscall_64+0x4f/0x260
[ 22.593424] entry_SYSCALL_64_after_hwframe+0x49/0xb3
[ 22.593852] RIP: 0033:0x7f3dc6874137
[ 22.594156] Code: 0b 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f
1f 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 2e 00 00 00 0f
05 <48> 3d 00 f0 ff ff 77 51 c3 48 83 ec 28 89 54 24 1c 48 89 74 24 10
[ 22.595809] RSP: 002b:00007ffd7df99488 EFLAGS: 00000246 ORIG_RAX:
000000000000002e
[ 22.596648] RAX: ffffffffffffffda RBX: 0000606000000200 RCX:
00007f3dc6874137
[ 22.597419] RDX: 0000000000000000 RSI: 00007ffd7df994f0 RDI:
0000000000000006
[ 22.598102] RBP: 00007ffd7df994f0 R08: 0000000000000004 R09:
0000000000000011
[ 22.598816] R10: 00007ffd7df99640 R11: 0000000000000246 R12:
00006070000250f0
[ 22.599449] R13: 00007ffd7df994f0 R14: 00007ffd7df99600 R15:
0000000000000000
