panic kexec broken on ARM64?

On Wed, 6 Jun 2018 11:06:28 +0530
Bhupesh Sharma [off-list ref] wrote:

Hello Petr,

On Tue, Jun 5, 2018 at 1:31 PM, Petr Tesarik [off-list ref] wrote:

quoted

Hi all,

I have observed hangs after crash on a Raspberry Pi 3 Model B+ board
when a panic kernel is loaded. I attached a hardware debugger and found
out that all CPU cores were stopped except one which was stuck in the
idle thread. It seems that irq_set_irqchip_state() may sleep, which is
definitely not safe after a kernel panic.  

[...]
Also do you get any console output from the crash kernel (you can try
passing earlycon to the crash kernel to see if it crashes early
enough)? If yes, can you please share the same.

Maybe I wasn't clear enough. The crashed kernel does not even get to
the kexec's purgatory code, so there cannot be any output from the
crash kernel.

[...]

quoted

#12 0xffff000001001cd0 in lan78xx_read_reg (index=152, data=0xffff000008e5396c <init_thread_union+14700>, dev=<optimized out>, dev=<optimized out>)
    at ../drivers/net/usb/lan78xx.c:425  

Hmmm, this seems a bit misplaced, but are you using a usb-ethernet
adapter which causes a URB submission to timeout?

Yes, RPi 3 B+ contains an on-board Microchip LAN7515, which is indeed a
USB device.

[...]

quoted

#26 0xffff000008081478 in do_mem_abort (addr=0, esr=2248146948, regs=0xffff000008e53d70 <init_thread_union+15728>) at ../arch/arm64/mm/fault.c:657
#27 0xffff000008082dd0 in el1_sync () at ../arch/arm64/kernel/entry.S:548  

The ESR value from the logs (2248146948) indicates the following about
the panic causes (see ARMv8 Architecture Reference Manual for more
details):

Thank you for all the detailx, but that's not relevant here. I am
crashing my system intentionally to debug the kexec/kdump
infrastructure...

Petr T