[PATCH] input/psmouse: Don't hold the mutex while calling ->disconnect

[Daniel Vetter <daniel.vetter@ffwll.ch>]

At least trackpoint_disconnect wants to remove some sysfs files, and
we can't remove sysfs files while holding psmouse_mutex:

======================================================
WARNING: possible circular locking dependency detected
4.16.0-rc5-g613eb885b69e-drmtip_1+ #1 Tainted: G     U
------------------------------------------------------
kworker/0:3/102 is trying to acquire lock:
 (kn->count#130){++++}, at: [<000000009679748b>] kernfs_remove_by_name_ns+0x3b/0x80

but task is already holding lock:
 (psmouse_mutex){+.+.}, at: [<0000000014f44bcc>] psmouse_disconnect+0x62/0x160

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (psmouse_mutex){+.+.}:
       psmouse_attr_set_helper+0x28/0x140
       kernfs_fop_write+0xfe/0x180
       __vfs_write+0x1e/0x130
       vfs_write+0xbd/0x1b0
       SyS_write+0x40/0xa0
       do_syscall_64+0x65/0x1a0
       entry_SYSCALL_64_after_hwframe+0x42/0xb7

-> #0 (kn->count#130){++++}:
       __kernfs_remove+0x243/0x2b0
       kernfs_remove_by_name_ns+0x3b/0x80
       remove_files.isra.0+0x2b/0x60
       sysfs_remove_group+0x38/0x80
       sysfs_remove_groups+0x24/0x40
       trackpoint_disconnect+0x2c/0x50
       psmouse_disconnect+0x8f/0x160
       serio_disconnect_driver+0x28/0x40
       serio_driver_remove+0xc/0x10
       device_release_driver_internal+0x15b/0x230
       serio_handle_event+0x1c8/0x260
       process_one_work+0x215/0x620
       worker_thread+0x48/0x3a0
       kthread+0xfb/0x130
       ret_from_fork+0x3a/0x50

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(psmouse_mutex);
                               lock(kn->count#130);
                               lock(psmouse_mutex);
  lock(kn->count#130);

 *** DEADLOCK ***

6 locks held by kworker/0:3/102:
 #0:  ((wq_completion)"events_long"){+.+.}, at: [<000000002e408bfa>] process_one_work+0x191/0x620
 #1:  (serio_event_work){+.+.}, at: [<000000002e408bfa>] process_one_work+0x191/0x620
 #2:  (serio_mutex){+.+.}, at: [<00000000c8a49847>] serio_handle_event+0x23/0x260
 #3:  (&dev->mutex){....}, at: [<00000000b55eee75>] device_release_driver_internal+0x2f/0x230
 #4:  (&serio->drv_mutex){+.+.}, at: [<000000009719f997>] serio_disconnect_driver+0x16/0x40
 #5:  (psmouse_mutex){+.+.}, at: [<0000000014f44bcc>] psmouse_disconnect+0x62/0x160

stack backtrace:
CPU: 0 PID: 102 Comm: kworker/0:3 Tainted: G     U           4.16.0-rc5-g613eb885b69e-drmtip_1+ #1
Hardware name: LENOVO 74591P0/74591P0, BIOS 6DET28WW (1.05 ) 07/30/2008
Workqueue: events_long serio_handle_event
Call Trace:
 dump_stack+0x5f/0x86
 print_circular_bug.isra.18+0x1d0/0x2c0
 __lock_acquire+0x14ae/0x1b60
 ? kernfs_remove_by_name_ns+0x20/0x80
 ? lock_acquire+0xaf/0x200
 lock_acquire+0xaf/0x200
 ? kernfs_remove_by_name_ns+0x3b/0x80
 __kernfs_remove+0x243/0x2b0
 ? kernfs_remove_by_name_ns+0x3b/0x80
 ? kernfs_name_hash+0xd/0x70
 ? kernfs_find_ns+0x7e/0x100
 kernfs_remove_by_name_ns+0x3b/0x80
 remove_files.isra.0+0x2b/0x60
 sysfs_remove_group+0x38/0x80
 sysfs_remove_groups+0x24/0x40
 trackpoint_disconnect+0x2c/0x50
 psmouse_disconnect+0x8f/0x160
 serio_disconnect_driver+0x28/0x40
 serio_driver_remove+0xc/0x10
 device_release_driver_internal+0x15b/0x230
 serio_handle_event+0x1c8/0x260
 process_one_work+0x215/0x620
 worker_thread+0x48/0x3a0
 ? _raw_spin_unlock_irqrestore+0x4c/0x60
 kthread+0xfb/0x130
 ? process_one_work+0x620/0x620
 ? _kthread_create_on_node+0x30/0x30
 ret_from_fork+0x3a/0x50

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Arvind Yadav <arvind.yadav.cs@gmail.com>
Cc: Stephen Lyons <slysven@virginmedia.com>
Cc: linux-input@vger.kernel.org
---
 drivers/input/mouse/psmouse-base.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/input/mouse/psmouse-base.c b/drivers/input/mouse/psmouse-base.c
index 8900c3166ebf..06ccd8e22f3c 100644
--- a/drivers/input/mouse/psmouse-base.c
+++ b/drivers/input/mouse/psmouse-base.c
@@ -1484,8 +1484,10 @@ static void psmouse_disconnect(struct serio *serio)
 		psmouse_deactivate(parent);
 	}
 
+	mutex_unlock(&psmouse_mutex);
 	if (psmouse->disconnect)
 		psmouse->disconnect(psmouse);
+	mutex_lock(&psmouse_mutex);
 
 	if (parent && parent->pt_deactivate)
 		parent->pt_deactivate(parent);
-- 
2.17.0