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 > > _______________________________________________ > Linuxppc-dev mailing list > Linuxppc-dev at lists.ozlabs.org > https://lists.ozlabs.org/listinfo/linuxppc-dev
