SEGFAULT when hotplugging a mouse and libinput is using udev as a backend

[ardera]

When libinput is using udev as a backend and a mouse is plugged in while flutter-pi is running, some time later a call to libinput_dispatch will result in a SEGFAULT because libinput somehow tries to invoke a function pointer that has a NULL value.

Are there any updates on this bug as it happens to me too.

If i use your raspberrypi-fast-ts in combination with a script to turn of the screen after n seconds per echo 1 | sudo tee /sys/class/backlight/rpi_backlight/bl_power the raspberrypi-fast-ts sometimes crashes because of an i2c error, the systemd service for it restarts it and than the flutter-pi crashes too.

So i guess the segv happens when ever the list of devices changes, either per usb-keyboard or per reinitialisation of the virtual-devices of raspberrypi-fast-ts after a restart of the service.

You can even force this error with the raspberrypi-fast-ts by

1. "systemctl disable raspberrypi-fast-ts.service" and
2. change config.txt to use the default touchscreen driver
3. reboort
4. after starting the flutter app
5. run "systemctl start raspberrypi-fast-ts".

Then you have a loop of flutter-app starting and crashing. (as long as you have configured the flutter-app to restart on failure per systemd service)

[ardera]

If i use your raspberrypi-fast-ts in combination with a script to turn of the screen after n seconds per echo 1 | sudo tee /sys/class/backlight/rpi_backlight/bl_power the raspberrypi-fast-ts sometimes crashes because of an i2c error, the systemd service for it restarts it and than the flutter-pi crashes too.

I should probably add some documentation for that, changing the backlight via the sysfs while raspberrypi-fast-ts is running causes the firmware and raspbian to try to use the I2C device concurrently, which can cause lots of problems. I'll add backlight supports for raspberrypi-fast-ts so you don't need to use the sysfs device.

I haven't debugged it thoroughly, but it seems to be caused by libinput itself. I'll look into it

fyi: is was using this library to turn the screen off: https://github.com/timothyhollabaugh/pi-touchscreen-timeout/blob/master/timeout.c

with gdb it says its a nullpointer dereferencing at the same address inside of libinput.
my guess is, with the change of available inputs (either by pluggin in/out a keyboard or restarting the raspberrypi-fast-ts service) the internal table of libinput for your handle gets invalid. a workaround could be to listen to those changes and before accessing libinput again to re-setup the connection to it.

[ardera]

my guess is, with the change of available inputs (either by pluggin in/out a keyboard or restarting the raspberrypi-fast-ts service) the internal table of libinput for your handle gets invalid. a workaround could be to listen to those changes and before accessing libinput again to re-setup the connection to it.

Libinput supports hotplugging, it'd be odd if it couldn't handle a simple device unplug.
It was actually a lot easier, I passed a stack pointer for the device open/close interface to libinput, because it was a const struct and I thought libinput would be copying it internally. It didn't.

tried it and it works. thx for the fast fix^^

fyi: running the flutter-pi with --no-text-input now causes a new segv (on keyboard plugging out/in)^^

Thread 1 "flutter-pi" received signal SIGSEGV, Segmentation fault.
0x00030e0c in keyboard_state_new (config=0x0, keymap_override=0x0, compose_table_override=0x0) at src/keyboard.c:263
xkb_state = xkb_state_new(keymap_override != NULL ? keymap_override : config->default_keymap);

(gdb) bt
#0 0x00030e0c in keyboard_state_new (config=0x0, keymap_override=0x0, compose_table_override=0x0) at src/keyboard.c:263
#1 0x0001c468 in on_libinput_ready (s=0x143a28, fd=9, revents=1, userdata=0x0) at src/flutter-pi.c:1962
#2 0x76ebd6a4 in () at /lib/arm-linux-gnueabihf/libsystemd.so.0

[ardera]

Thread 1 "flutter-pi" received signal SIGSEGV, Segmentation fault.
0x00030e0c in keyboard_state_new (config=0x0, keymap_override=0x0, compose_table_override=0x0) at src/keyboard.c:263
xkb_state = xkb_state_new(keymap_override != NULL ? keymap_override : config->default_keymap);

Thanks, fixed it. Though I should really just remove the --no-text-input flag. It was useful when flutter-pi was still using stdin for text/keyboard input, since it would switch it to raw/non-canonical mode which could cause problems on some occasions. Now, flutter-pi uses libinput for keyboard input, and converts the keyboard input to text input using libxkbcommon and the /etc/default/keyboard config file, so text input doesn't cause problems anymore.

thx again for the fast response. keep up the good work^^