Fix deadlocks in autosuspend

Marcus Folkesson
2018-02-28T13:38:15Z

Hello,

I have not recieved any feedback on these so I resend them.

I got this deadlock on my own driver (pxrc) when using the same
construction.

Please have a look

Here is a clip from
[PATCH v3] input: pxrc: new driver for PhoenixRC Flight Controller Adapter [1]
that describes the problem.

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Also, I think we have a deadlock in the synaptics_usb driver.

When the device is suspended and someone is open the device, the input
subsystem will call input_open_device() which takes the
input_dev->mutex and then call input_dev->open().

synusb_open() has a call to usb_autopm_get_interface() which will
result in a call to the registered resume-function if the device is
suspended. (see Documentation/driver-api/usb/power-manaement.rst).

In the case of snaptics_usb, it will take the input_dev->mutex in the
resume function.

I have no synaptic mouse, but tested to put the same code into my
driver just to confirm, and got the following dump:

[ 9215.626476] INFO: task input-events:8590 blocked for more than 120 seconds.
[ 9215.626495] Not tainted 4.15.0-rc8-ARCH+ #6
[ 9215.626500] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 9215.626507] input-events D 0 8590 4394 0x00000004
[ 9215.626520] Call Trace:
[ 9215.626546] ? __schedule+0x236/0x850
[ 9215.626559] schedule+0x2f/0x90
[ 9215.626569] schedule_preempt_disabled+0x11/0x20
[ 9215.626579] __mutex_lock.isra.0+0x1aa/0x520
[ 9215.626609] ? usb_runtime_suspend+0x70/0x70 [usbcore]
[ 9215.626622] ? pxrc_resume+0x37/0x70 [pxrc]
[ 9215.626632] pxrc_resume+0x37/0x70 [pxrc]
[ 9215.626655] usb_resume_interface.isra.2+0x39/0xe0 [usbcore]
[ 9215.626676] usb_resume_both+0xd2/0x120 [usbcore]
[ 9215.626688] __rpm_callback+0xb6/0x1f0
[ 9215.626699] rpm_callback+0x1f/0x70
[ 9215.626718] ? usb_runtime_suspend+0x70/0x70 [usbcore]
[ 9215.626726] rpm_resume+0x4e2/0x7f0
[ 9215.626737] rpm_resume+0x582/0x7f0
[ 9215.626749] __pm_runtime_resume+0x3a/0x50
[ 9215.626767] usb_autopm_get_interface+0x1d/0x50 [usbcore]
[ 9215.626780] pxrc_open+0x17/0x8d [pxrc]
[ 9215.626791] input_open_device+0x70/0xa0
[ 9215.626804] evdev_open+0x183/0x1c0 [evdev]
[ 9215.626819] chrdev_open+0xa0/0x1b0
[ 9215.626830] ? cdev_put.part.1+0x20/0x20
[ 9215.626840] do_dentry_open+0x1ad/0x2c0
[ 9215.626855] path_openat+0x576/0x1300
[ 9215.626868] ? alloc_set_pte+0x22c/0x520
[ 9215.626883] ? filemap_map_pages+0x19b/0x340
[ 9215.626893] do_filp_open+0x9b/0x110
[ 9215.626908] ? __check_object_size+0x9d/0x190
[ 9215.626920] ? __alloc_fd+0xaf/0x160
[ 9215.626931] ? do_sys_open+0x1bd/0x250
[ 9215.626942] do_sys_open+0x1bd/0x250
[ 9215.626956] entry_SYSCALL_64_fastpath+0x20/0x83
[ 9215.626967] RIP: 0033:0x7fbf6358f7ae

tablet/pegasus_notetaker.c and touchscreen/usbtouchscreen.c has the same
construction (taking input_dev->mutex in resume/suspend and call
usb_autopm_get_interface() in open()).

I will create a separate "pm_mutex" to use instead of input_dev->mutex
to get rid of the lockups in those drivers

-------------------------------8<----------------------------------------------

[1] https://lkml.org/lkml/2018/1/20/191

Thanks,

Best regards
Marcus Folkesson