On 08.10.19 22:18, Qian Cai wrote: > The linux-next series "mm/memory_hotplug: Shrink zones before removing memory" > [1] causes a kernel panic while reading /proc/kpagecount after offlining a > memory section. It was reproduced on both x86 and powerpc. Reverted the whole > series fixed the problem. > > [1] https://lore.kernel.org/linux-mm/20191006085646.5768-1-david@xxxxxxxxxx/ > > # echo offline > /sys/devices/system/memory/memory124/state > # cat /proc/kpagecount > > [ 133.268032][ T8809] remove from free list 7c000 256 7d000 > [ 133.268134][ T8809] remove from free list 7c100 256 7d000 > [ 133.268153][ T8809] remove from free list 7c200 256 7d000 > [ 133.268182][ T8809] remove from free list 7c300 256 7d000 > [ 133.268212][ T8809] remove from free list 7c400 256 7d000 > [ 133.268241][ T8809] remove from free list 7c500 256 7d000 > [ 133.268260][ T8809] remove from free list 7c600 256 7d000 > [ 133.268289][ T8809] remove from free list 7c700 256 7d000 > [ 133.268329][ T8809] remove from free list 7c800 256 7d000 > [ 133.268359][ T8809] remove from free list 7c900 256 7d000 > [ 133.268399][ T8809] remove from free list 7ca00 256 7d000 > [ 133.268429][ T8809] remove from free list 7cb00 256 7d000 > [ 133.268458][ T8809] remove from free list 7cc00 256 7d000 > [ 133.268488][ T8809] remove from free list 7cd00 256 7d000 > [ 133.268517][ T8809] remove from free list 7ce00 256 7d000 > [ 133.268546][ T8809] remove from free list 7cf00 256 7d000 > [ 133.268580][ T8809] Offlined Pages 4096 > [ 144.038732][ T8944] BUG: Unable to handle kernel data access at > 0xfffffffffffffffe > [ 144.038769][ T8944] Faulting instruction address: 0xc000000000590c08 > [ 144.038794][ T8944] Oops: Kernel access of bad area, sig: 11 [#1] > [ 144.038807][ T8944] LE PAGE_SIZE=64K MMU=Radix MMU=Hash SMP NR_CPUS=256 > DEBUG_PAGEALLOC NUMA PowerNV > [ 144.038822][ T8944] Modules linked in: ip_tables x_tables xfs sd_mod bnx2x > mdio ahci libahci tg3 libata libphy firmware_class dm_mirror dm_region_hash > dm_log dm_mod > [ 144.038864][ T8944] CPU: 116 PID: 8944 Comm: cat Not tainted 5.4.0-rc2+ #6 > [ 144.038898][ T8944] NIP: c000000000590c08 LR: c000000000577330 CTR: > c0000000005909d0 > [ 144.038945][ T8944] REGS: c00020196bd6fa30 TRAP: 0380 Not tainted (5.4.0- > rc2+) > [ 144.038989][ T8944] MSR: 9000000000009033 <SF,HV,EE,ME,IR,DR,RI,LE> CR: > 48022428 XER: 20040000 > [ 144.039028][ T8944] CFAR: c000000000590ad0 IRQMASK: 0 > [ 144.039028][ T8944] GPR00: c000000000577330 c00020196bd6fcc0 c000000001122d00 > c0002009d3d4a880 > [ 144.039028][ T8944] GPR04: 00007fffb6870000 0000000000020000 fffffffffffffffe > c00c000000000000 > [ 144.039028][ T8944] GPR08: 0000000001f00000 c00c000001f00000 0000000000000001 > c0000000009413d0 > [ 144.039028][ T8944] GPR12: c0000000005909d0 c000201fff677000 0000000000000000 > 0000000000000000 > [ 144.039028][ T8944] GPR16: 0000000000000002 00007fffca34cfa8 ffffffffffffffff > 0000000000000000 > [ 144.039028][ T8944] GPR20: 0000000000000000 0000000000000000 c000000000000000 > c00020196bd6fdf0 > [ 144.039028][ T8944] GPR24: 00007fffb6870000 0000000007ffffff 0000000000000000 > c000000000aa6c20 > [ 144.039028][ T8944] GPR28: 00007fffb6890000 0000000000000008 000000000007c000 > 00007fffb6870000 > [ 144.039240][ T8944] NIP [c000000000590c08] kpagecount_read+0x238/0x3f0 > [ 144.039263][ T8944] LR [c000000000577330] proc_reg_read+0x90/0x130 > [ 144.039274][ T8944] Call Trace: > [ 144.039304][ T8944] [c00020196bd6fd30] [c000000000577330] > proc_reg_read+0x90/0x130 > [ 144.039342][ T8944] [c00020196bd6fd60] [c0000000004978bc] > __vfs_read+0x3c/0x70 > [ 144.039377][ T8944] [c00020196bd6fd80] [c00000000049799c] vfs_read+0xac/0x170 > [ 144.039423][ T8944] [c00020196bd6fdd0] [c000000000497dfc] > ksys_read+0x7c/0x140 > [ 144.039472][ T8944] [c00020196bd6fe20] [c00000000000b378] > system_call+0x5c/0x68 > [ 144.039495][ T8944] Instruction dump: > [ 144.039513][ T8944] 4e800020 60000000 3d22000d 3929c098 7bc83664 e8e90000 > 7d274215 418200ac > [ 144.039540][ T8944] e9490008 38caffff 714a0001 7cc9309e <e9460000> 2faaffff > e9490008 419e00fc > [ 144.039580][ T8944] ---[ end trace 96fb2ea2d503fda9 ]--- > [ 144.492072][ T8944] > [ 145.492172][ T8944] Kernel panic - not syncing: Fatal exception > Thanks, that's somewhat expected as I taint pages more aggressively. It's a pre-existing issue. You can trigger the exact same BUG by 1. Hotplugging a DIMM but not onlining it 2. cat /proc/kpagecount The right fix is to add a pgn_to_online_page() to the PFN walker and skip all PFNs that are not online. This was already discussed in the context of ZONE_DEVICE and I am yet waiting for a fix. I can prepare and send a fix for that PFN walker tomorrow. -- Thanks, David / dhildenb
