Handling spin table in kdump

[McClintock Matthew-B29882]

On Tue, May 22, 2012 at 7:42 AM, Suzuki K. Poulose <suzuki at in.ibm.com> wrote:
> Hi
>
> I came across the following issue while testing Kdump on an SMP
> board(Currituck) running a non-SMP kernel. Even though the kernel is UP,
> the device-tree has the nodes for second CPU and the related details.
>
>
> The kexec tool adds the spin table area as a reserved section in the device
> tree for the dump capture kernel. This value is read from the
> 'cpu-release-addr'.
>
> But now, if the spin table is not located within the 'Reserved region' for
> the crash kernel, the dump capture kernel would fail to boot, hitting a BUG
> in mm/bootmem.c as in [1].
>
> This is because we try to reserve a region which is not available to the
> kernel.
>
> So I am wondering how is this handled really on an SMP board (Fsl_bookE).
>
> There are two possible solutions :
> 1) Do not reserve the regions for the spin-table, as we will use
> only the crashing CPU in the second kernel(maxcpus=1).
>
>
> 2) Add the spin-table region to the available memory regions passed
> to the kernel by kexec-tools.
>
> I have tested (1) and it works fine for me. Yet to test (2).
>
>
> Thoughts ?

I would think option 1 is acceptable. The crash kernel will never
attempt to use the memory outside of the crash kernel region therefore
it does not need to be reserved.

However, I thought we were able to boot SMP into the crash kernel on
our parts... not sure how that effects things (although the maxcpus=1
here is a perfectly acceptable and safer thing to do anyways)

-M


>
>
> Thanks
> Suzuki
>
>
>
> [1] Kernel Bug
> ----------------
>
>
> Linux version 3.3.0-rc5 (root at suzukikp.in.ibm.com) (gcc version 4.3.4
> [gcc-4_3-branch revision 152973] (GCC) ) #12 Tue May 22 18:03:01 IST2
> Found legacy serial port 0 for /plb/opb/serial at 10000000
>  mem=20010000000, taddr=20010000000, irq=0, clk=1851851, speed=115200
> ------------[ cut here ]------------
> kernel BUG at mm/bootmem.c:351!
> Vector: 700 (Program Check) at [c8a61e90]
>    pc: c847f91c: mark_bootmem+0xa0/0x14c
>    lr: c8472670: do_init_bootmem+0x1ac/0x218
>    sp: c8a61f40
>   msr: 21000
>  current = 0xc8a4a500
>    pid   = 0, comm = swapper
> kernel BUG at mm/bootmem.c:351!
> enter ? for help
> [c8a61f70] c8472670 do_init_bootmem+0x1ac/0x218
> [c8a61f90] c847025c setup_arch+0x1bc/0x234
> [c8a61fb0] c846b62c start_kernel+0x98/0x358
> [c8a61ff0] c80000b4 _start+0xb4/0xf8
>
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