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Subjectlockdep warning on thunderbolt docking
When connecting a thunderbolt-enabled docking station to my work laptop,
the following lockdep warning is reported on v5.3.0-rc6+ as of Thursday
morning (can look up the exact git id if so required):


thunderbolt 0-1: new device found, vendor=0xd4 device=0xb070
thunderbolt 0-1: Dell WD19TB Thunderbolt Dock

======================================================
WARNING: possible circular locking dependency detected
5.3.0-rc6+ #1 Tainted: G T
------------------------------------------------------
pool-/usr/lib/b/1258 is trying to acquire lock:
000000005ab0ad43 (pci_rescan_remove_lock){+.+.}, at: authorized_store+0xe8/0x210

but task is already holding lock:
00000000bfb796b5 (&tb->lock){+.+.}, at: authorized_store+0x7c/0x210

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (&tb->lock){+.+.}:
__mutex_lock+0xac/0x9a0
tb_domain_add+0x2d/0x130
nhi_probe+0x1dd/0x330
pci_device_probe+0xd2/0x150
really_probe+0xee/0x280
driver_probe_device+0x50/0xc0
bus_for_each_drv+0x84/0xd0
__device_attach+0xe4/0x150
pci_bus_add_device+0x4e/0x70
pci_bus_add_devices+0x2e/0x66
pci_bus_add_devices+0x59/0x66
pci_bus_add_devices+0x59/0x66
enable_slot+0x344/0x450
acpiphp_check_bridge.part.0+0x119/0x150
acpiphp_hotplug_notify+0xaa/0x140
acpi_device_hotplug+0xa2/0x3f0
acpi_hotplug_work_fn+0x1a/0x30
process_one_work+0x234/0x580
worker_thread+0x50/0x3b0
kthread+0x10a/0x140
ret_from_fork+0x3a/0x50

-> #0 (pci_rescan_remove_lock){+.+.}:
__lock_acquire+0xe54/0x1ac0
lock_acquire+0xb8/0x1b0
__mutex_lock+0xac/0x9a0
authorized_store+0xe8/0x210
kernfs_fop_write+0x125/0x1b0
vfs_write+0xc2/0x1d0
ksys_write+0x6c/0xf0
do_syscall_64+0x50/0x180
entry_SYSCALL_64_after_hwframe+0x49/0xbe

other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&tb->lock);
lock(pci_rescan_remove_lock);
lock(&tb->lock);
lock(pci_rescan_remove_lock);

*** DEADLOCK ***
5 locks held by pool-/usr/lib/b/1258:
#0: 000000003df1a1ad (&f->f_pos_lock){+.+.}, at: __fdget_pos+0x4d/0x60
#1: 0000000095a40b02 (sb_writers#6){.+.+}, at: vfs_write+0x185/0x1d0
#2: 0000000017a7d714 (&of->mutex){+.+.}, at: kernfs_fop_write+0xf2/0x1b0
#3: 000000004f262981 (kn->count#208){.+.+}, at: kernfs_fop_write+0xfa/0x1b0
#4: 00000000bfb796b5 (&tb->lock){+.+.}, at: authorized_store+0x7c/0x210

stack backtrace:
CPU: 0 PID: 1258 Comm: pool-/usr/lib/b Tainted: G T 5.3.0-rc6+ #1


Thanks,
Dominik

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