Re: lockdep warning on thunderbolt docking

[Mika Westerberg]

Hi Dominik,

On Fri, Aug 30, 2019 at 02:58:48PM +0200, Dominik Brodowski wrote:
> 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):

Thanks for reporting. No need to dig for the commit ID.

I'll take a look at this next week.

> 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