When soft reboot Linux kernel hangs at "Uncompressing Linux... done, booting the kernel" [closed]

Question

I am using Linux kernel 3.0.21 on my custom hardware.

• when I first start hardware, it successfully boots up.

• if I shut down properly and again start hardware, it succesfully boots up.

But once the system is up running, when I type reboot command restarts the kernel and hangs at

Starting kernel ...

Uncompressing Linux... done, booting the kernel.

I dont know why I am facing this on each soft reboot. To avoid this I need to hard reset (power off and power on again).

Why I am facing this issue? Is there any clean up function missing in kernel? How to debug this issue?

Answer 1

Yes, it sounds like somewhere in the platform support for you hardware you are missing some logic to cope with a soft reboot.

Adding clean-up code doesn't solve the problem, because the system may crash, and then be soft rebooted.

So the code that boots up the system needs to be written to cope with the system being soft rebooted.

To debug you'll first need to find out where the kernel is getting stuck during the soft reboot. The easiest way to do that is with a hardware debugger.

The other option is to read through the boot up code and try and spot any areas that might be relying on a cold reboot to work, eg. code that expects the TLB to be cleared at boot or similar.

Answer 2

Sounds like a failure to neutralise the hardware before rebooting. Likely candidates are MMU, TLB, caches or interrupts. The crash will occur early in kernel boot when these are re-enabled (this may be the kernel failing to disable them all before reboot, or the boot-loader relying on hard-reset state which of course you don't get on soft-reset).

As others have indicated a JTAG hardware debug probe is just about the only way you're going t get to the bottom of this one.