Recovery from unresponsive system

[mthuurne]

Sometimes the system might become unresponsive and no telnet connection or way to press the reset pin is near. We should have one or more measures to regain control of the system.

There are different unresponsive situations that need to be handled separately:

• If the kernel has crashed and not paniced, for example by overclocking too high, there is nothing we can do: reset is the only way out.
• If the kernel has paniced, we can use the feature to automatically reboot on panics.
• If the kernel is still running but the userland is broken beyond repair, a forced reboot is useful. This would be similar to "eisub" ("reisub" without "r", see Magic SysRq).
• If the application that controls the current virtual terminal is hanging, killing that application would return control to the menu and make the system responsive again. This is probably the most common kind of unresponsiveness.

[mthuurne]

Actually, we can use the watch dog timer feature of the JZ4740 to automatically restart the system if the kernel is no longer responding.

[mthuurne]

Ayla wrote a watchdog driver for the JZ4740. It should be integrated in the OpenDingux kernel and be activated and sent "still alive" signals from user space. This could either be done using a dedicated daemon or from the power slider daemon. A dedicated daemon is the cleaner solution, but we have to check what the impact is on memory use.

The feature to kill the application that uses the current virtual terminal could be implemented in either the kernel or the power slider daemon. I prefer the daemon, since we could add visual confirmation to that once we have the overlay framebuffer.

[mthuurne]

Current status: Watchdog is integrated and the rootfs starts a daemon for it. Auto-reboot on panic is enabled. The power slider daemon has button combinations for reboot and poweroff. What is still missing is a forced reboot when user space is half-functional (watchdog operational but "reboot" command not working) and a way to terminate the active application.

[pcercuei]

It is now possible to kill the active application via a key shortcut.