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How to debug kernel panic on kernel 4.12.28?

Posted by Bali 
I am trying to debug the embedded Linux kernel 4.12.28, this crashes and shows kernel panic. I have put some prints inside blocks/genhd.c to print the disk_name. I see that it crashes inside - "bdget_disk" while getting the bdgt_disk for disk_name "ram0". I am using a power pc architecture. I am a bit puzzled on how should I approach this issue or how can I debug? I am unable to understand the root cause. My understanding is that ram0 is like a RAM disk needed for initial bootup by the system. The initrd contents will be copied to ram0 for bootup. I don't understand why it crashes. I can make out that it is related to bad address. But what is the real reason and how to
debug this?

My defconfig has -


The kernel panic logs are -

Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled
    serial8250.0: ttyS0 at MMIO 0xe0004500 (irq = 16, base_baud = 19531250) is a 16550A
    serial8250.0: ttyS1 at MMIO 0xe0004600 (irq = 17, base_baud = 19531250) is a 16550A
    console [ttyS1] enabled
    console [ttyS1] enabled
    bootconsole [udbg0] disabled
    bootconsole [udbg0] disabled
    Custom Debug..DEBUG: Passed bdget_disk 765
    Custom Debug.. the disc name is ram0
    Unable to handle kernel paging request for data at address 0x00005484
    Faulting instruction address: 0xc0100154
    Oops: Kernel access of bad area, sig: 11 [#1]
    Modules linked in:
    CPU: 0 PID: 1 Comm: swapper Not tainted 4.12.28-biamp-standard #1
    task: df416a60 task.stack: df42a000
    NIP: c0100154 LR: c011d158 CTR: c02bd990
    REGS: df42bcb0 TRAP: 0300   Not tainted  (4.12.28-biamp-standard)
    MSR: 00009032 <EE,ME,IR,DR,RI>
      CR: 242c0484  XER: 00000000
    DAR: 00005484 DSISR: 20000000
    GPR00: c02406bc df42bd60 df416a60 df407800 00000001 c011cb4c c011cb64 df42bd68
    GPR08: 00000005 00000001 c0660000 00000000 222c0824 00000000 c00040f0 00000000
    GPR16: 00000000 00000000 00000000 00000000 00000000 00000000 c0660000 c05fa2dc
    GPR24: 00000007 00000093 df50d00c df50d060 00000000 df50d058 00000000 df50d040
    NIP [c0100154] iget5_locked+0xc/0x250
    LR [c011d158] bdget+0x40/0xf4
    Call Trace:
    [df42bd60] [c0652708] log_wait+0x0/0x8 (unreliable)
    [df42bd80] [c02406bc] bdget_disk+0xac/0xf8
    [df42bda0] [c0241780] device_add_disk+0x3f4/0x43c
    [df42bdf0] [c060ed5c] brd_init+0xa8/0x184
    [df42be20] [c0003a5c] do_one_initcall+0x48/0x18c
    [df42be90] [c05faafc] kernel_init_freeable+0x130/0x228
    [df42bf20] [c0004108] kernel_init+0x18/0x110
    [df42bf40] [c00103f0] ret_from_kernel_thread+0x5c/0x64
    Instruction dump:
    741d7e44 3f090d7e ea9463ef 3a7ebecd fc607969 24b8044d a251c1c7 2c91258b
    242aaa92 9887d4e0 2f4a22b5 8b2ef93c <8b9c5484> 7ecf225d 6a9c4a5b 1a5791d4
    ---[ end trace 47ca8dc77d8de71b ]---
    Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
    Rebooting in 180 seconds..

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