Re: Fix deadlocks in autosuspend

[Marcus Folkesson]

Ping.

Would someone please have a look?

Thanks,
Marcus Folkesson

On Wed, Feb 28, 2018 at 02:37:57PM +0100, Marcus Folkesson wrote:
> 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.
> 
> -------------------------------8<----------------------------------------------
> 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
>

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