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SubjectRe: psmouse_disconnect lockdep splat
On Tue, Oct 18, 2016 at 02:09:22PM +0200, Borislav Petkov wrote:
> Adding more people to CC.
>
> I still see this after 4.8 is out.
>
> So PeterZ suggested something like this:
>
> ---
> diff --git a/drivers/input/mouse/psmouse-base.c b/drivers/input/mouse/psmouse-base.c
> index fb4b185dea96..9112c3cecad7 100644
> --- a/drivers/input/mouse/psmouse-base.c
> +++ b/drivers/input/mouse/psmouse-base.c
> @@ -1420,14 +1420,16 @@ static void psmouse_disconnect(struct serio *serio)
> psmouse_deactivate(parent);
> }
>
> - if (psmouse->disconnect)
> - psmouse->disconnect(psmouse);
> -
> if (parent && parent->pt_deactivate)
> parent->pt_deactivate(parent);
>
> psmouse_set_state(psmouse, PSMOUSE_IGNORE);
>
> + mutex_unlock(&psmouse_mutex);
> + if (psmouse->disconnect)
> + psmouse->disconnect(psmouse);
> + mutex_lock(&psmouse_mutex);
> +
> serio_close(serio);
> serio_set_drvdata(serio, NULL);
> input_unregister_device(psmouse->dev);
> ---
>
> to fix the lock inversion but that might have the other problem of
> being racy by maybe ->reconnect() accessing psmouse->private in
> trackpoint_sync() outside of the psmouse_mutex lock and that won't be
> nice.
>
> But someone more knowledgeable with this code should take a look and
> suggest a proper fix.
>
> Thanks!
>
> (Leaving in the rest for reference).

The splat still persists on up-to-date kernel. See below. That's for
current -tip tree, but it's in mainline too.

Nobody cares?

======================================================
WARNING: possible circular locking dependency detected
4.14.0-rc6-00555-g34aa400565bc #151 Tainted: G W
------------------------------------------------------
kworker/0:1/38 is trying to acquire lock:
(kn->count#188){++++}, at: [<ffffffff8233ba60>] kernfs_remove_by_name_ns+0x40/0x80

but task is already holding lock:
(psmouse_mutex){+.+.}, at: [<ffffffff82805b37>] psmouse_disconnect+0x67/0x160

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (psmouse_mutex){+.+.}:
__mutex_lock+0x85/0x960
psmouse_attr_set_helper+0x2d/0x140
kernfs_fop_write+0x112/0x1a0
__vfs_write+0x23/0x130
vfs_write+0xc9/0x1d0
SyS_write+0x45/0xb0
entry_SYSCALL_64_fastpath+0x23/0xc2

-> #0 (kn->count#188){++++}:
lock_acquire+0xc1/0x220
__kernfs_remove+0x248/0x2b0
kernfs_remove_by_name_ns+0x40/0x80
remove_files.isra.0+0x31/0x70
sysfs_remove_group+0x3d/0x80
trackpoint_disconnect+0x20/0x40
psmouse_disconnect+0x94/0x160
serio_disconnect_driver+0x2d/0x40
serio_driver_remove+0x11/0x20
device_release_driver_internal+0x160/0x230
serio_reconnect_subtree+0x4a/0xa0
serio_handle_event+0x1af/0x270
process_one_work+0x1ea/0x680
worker_thread+0x4d/0x3e0
kthread+0x145/0x180
ret_from_fork+0x2a/0x40

other info that might help us debug this:

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(psmouse_mutex);
lock(kn->count#188);
lock(psmouse_mutex);
lock(kn->count#188);

*** DEADLOCK ***

6 locks held by kworker/0:1/38:
#0: ((wq_completion)"events_long"){+.+.}, at: [<ffffffff8210f705>] process_one_work+0x165/0x680
#1: (serio_event_work){+.+.}, at: [<ffffffff8210f705>] process_one_work+0x165/0x680
#2: (serio_mutex){+.+.}, at: [<ffffffff827f3271>] serio_handle_event+0x21/0x270
#3: (&dev->mutex){....}, at: [<ffffffff826e9ac4>] device_release_driver_internal+0x34/0x230
#4: (&serio->drv_mutex){+.+.}, at: [<ffffffff827f235b>] serio_disconnect_driver+0x1b/0x40
#5: (psmouse_mutex){+.+.}, at: [<ffffffff82805b37>] psmouse_disconnect+0x67/0x160

stack backtrace:
CPU: 0 PID: 38 Comm: kworker/0:1 Tainted: G W 4.14.0-rc6-00555-g34aa400565bc #151
Hardware name: LENOVO 20FXS09D2P/20FXS09D2P, BIOS R07ET71W (2.11 ) 09/26/2016
Workqueue: events_long serio_handle_event
Call Trace:
dump_stack+0x7c/0xbe
print_circular_bug+0x202/0x380
? lockdep_init_map_crosslock+0x20/0x20
check_prev_add+0x43f/0x7b0
? __lock_acquire+0x133d/0x1550
__lock_acquire+0x133d/0x1550
lock_acquire+0xc1/0x220
? kernfs_remove_by_name_ns+0x40/0x80
__kernfs_remove+0x248/0x2b0
? kernfs_remove_by_name_ns+0x40/0x80
? kernfs_name_hash+0x12/0x80
? kernfs_find_ns+0x89/0x100
kernfs_remove_by_name_ns+0x40/0x80
remove_files.isra.0+0x31/0x70
sysfs_remove_group+0x3d/0x80
trackpoint_disconnect+0x20/0x40
psmouse_disconnect+0x94/0x160
serio_disconnect_driver+0x2d/0x40
serio_driver_remove+0x11/0x20
device_release_driver_internal+0x160/0x230
serio_reconnect_subtree+0x4a/0xa0
serio_handle_event+0x1af/0x270
process_one_work+0x1ea/0x680
worker_thread+0x4d/0x3e0
kthread+0x145/0x180
? process_one_work+0x680/0x680
? kthread_create_on_node+0x40/0x40
ret_from_fork+0x2a/0x40
--
Kirill A. Shutemov

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