(+ Marc) On 1 November 2018 at 22:14, Bhupesh Sharma <bhsharma@xxxxxxxxxx> wrote: > Hi, > > With the latest EFI changes for memblock reservation across kdump > kernel from Ard (Commit 71e0940d52e107748b270213a01d3b1546657d74 > ["efi: honour memory reservations passed via a linux specific config > table"]), we hit a panic while trying to boot the kdump kernel on > machines which have large number of CPUs. > Just for my understanding: why do you boot all 224 CPus when running the crash kernel? I'm not saying we shouldn't fix the underlying issue, I'm just curious. > I have a arm64 board which has 224 CPUS: > # lscpu > <..snip..> > CPU(s): 224 > On-line CPU(s) list: 0-223 > <..snip..> > > Here are the crash logs in the kdump kernel on this machine: > > [ 0.000000] Unable to handle kernel paging request at virtual > address ffff80003ffe0000 > val____)nt EL), IL ata abort info: > [ 0.or: Oops: 960000inted 4.18.0+ #3 > [ 0.000000] pstate: 20400089 (nzCv daIf +PAN -UAO) > [ 0.000000] pc : __memcpy+0x110/0x180 > [ 0.000000] lr : memblock_double_array+0x240/0x348 > [ 0.000000] sp : ffff0000092efc80 x28: 00000000bffe0000 > [ 0.000000] x27: 0000000000001800 x26: ffff000009d59000 > [ 0.000000] x25: ffff80003ffe0000 x24: 0000000000000000 > [ 0.000000] x23: 0000000000010000 x22: ffff000009d594e8 > [ 0.000000] x21: ffff000009d594f4 x20: ffff0000093c7268 > [ 0.000000] x19: 0000000000000c00 x18: 0000000000000010 > [ 0.000000] x17: 0000000000000000 x16: 0000000000000000 > [ 0.000000] x15: ffffffffffffffff3: 0000000fc18d0000 x12: 0000000800000000 > [ 0.000000] x11: 0000000000000018 x10: 00000000ddab9e18 > [ 0.000000] x9 : 0000000800000000 x8 : 00000000000002c1 > [ 0.000000] x7 : 0000000091b90000 x6 : ffff80003ffe0000 > [ 0.000000] x5 : 0000000000000001 x4 : 0000000000000000 > [ 0.000000] x3 : 0000000000000000 x2 : 0000000000000b80 > [ 0.000000] x1 : ffff000009d59540 x0 : ffff80003ffe0000 > [ 0.000000] Process swapper) > [ 0.000000] Call trace: > [ 0.000000] __memcpy+0x110/0x180 > [ 0.000000] memblock_add_range+0x134/0x2e8 > [ 0.000000] memblock_reserve+0x70/0xb8 > [ 0.000000] memblock_alloc_base_nid+0x6c/0x88 > [ 0.000000] __memblock_alloc_base+0x3c/0x4c > [ 0.000000] memblock_alloc_base+0x28/0x4c > [ 0.000000] memblock_alloc+0x2c/0x38 > [ 0.000000] early_pgtable_alloc+0x20/0xb0 > [ 0.000000] paging_init+0x28/0x7f8 > [ 0.000000] start_kernel+0x78/0x4cc > [ 0.000000] Code: a8c12027 a8c12829 a8c1302b a8c1382d (a88120c7) > [ 0.000000] random: get_random_bytes called from > print_oops_end_marker+0x30/0x58 with crng_init=0 > [ 0.000000] ---[ end trace 0000000000000000 ]--- > [ 0.000000] Kernel panic - not syncing: Fatal exception > [ 0.000000] ---[ end Kernel panic - not syncing: Fatal exception ]--- > > Adding more debug logs via 'memblock=debug' being passed to the kdump > kernel, (and adding a few more prints to 'mm/memblock.c'), I can see > that the panic happens while trying to resize array inside > 'memblock_double_array' (which doubles the size of the memblock > regions array): > > [ 0.000000] Reserving 13KB of memory at 0xbfff0000 for elfcorehdr > [ 0.000000] memblock_reserve: > [0x00000000bfff0000-0x00000000bfffffff] > memblock_alloc_base_nid+0x6c/0x88 > [ 0.000000] memblock: use_slab is 0, new_area_start=bfff0000, > new_area_size=10000 > [ 0.000000] memblock: use_slab is 0, addr=0, new_area_size=10000 > [ 0.000000] memblock: addr=bffe0000, __va(addr)=ffff80003ffe0000 > [ 0.00000 [0xbffe0000-0xbffe17ff] > [ 0.000000] Unable to handle kernel paging request at virtual > address ffff80003ffe0000 > > which indicates that after Ard's patch the memblocks being reserved > across kdump swell up on systems which have large number of CPUs and > hence 'memblock_double_array' is called up in early kdump boot code to > double the size of the memblock regions array. > > To confirm the above, I reduced the number of SMP CPUs available to > the kernel on this system, by specifying 'nr_cpus=46' in the kernel > bootargs for the primary kernel. As expected this makes the kdump > kernel boot successfully and also save the crash dump properly. > > I saw another arm64 kdump user report this issue to me privately, so I > am sending this to a wider audience, so that kdump users are aware > that this is a known issue. > > I am working on a RFC patch which seems to fix the issue on my board > and will try to send it out for wider review in coming days after some > more checks at my end. > > Any advices on the same are also welcome :) > > Thanks, > Bhupesh
