On Sat, 10 Jul 2021, Igor Raits wrote:

> Hello,
>
> I've seen one weird bug on 5.12.14 that happened a couple of times when I
> started a bunch of VMs on a server.

Would it be possible for you to try the same on a 5.12.13 kernel?
Perhaps by reverting the diff between 5.12.13 and 5.12.14 temporarily.
Enough to form an impression of whether the issue is new in 5.12.14.

I ask because 5.12.14 did include several fixes and cleanups from me
to page_vma_mapped_walk(), and that is involved in inserting and
removing pmd migration entries.  I am not aware of introducing any
bug there, but your report has got me worried.  If it's happening in
5.12.14 but not in 5.12.13, then I must look again at my changes.

I don't expect Hillf's patch to help at at all: the pmd_lock()
is supposed to be taken by page_vma_mapped_walk(), before
set_pmd_migration_entry() and remove_migration_pmd() are called.

Thanks,
Hugh

>
> I've briefly googled this problem but could not find any relevant commit
> that would fix this issue.
>
> Do you have any hint how to debug this further or know the fix by any
> chance?
>
> Thanks in advance. Stack trace following:
>
> [  376.876610] ------------[ cut here ]------------
> [  376.881274] kernel BUG at include/linux/swapops.h:204!
> [  376.886455] invalid opcode: 0000 [#1] SMP NOPTI
> [  376.891014] CPU: 40 PID: 11775 Comm: rpc-worker Tainted: G            E
>     5.12.14-1.gdc.el8.x86_64 #1
> [  376.900464] Hardware name: HPE ProLiant DL380 Gen10/ProLiant DL380
> Gen10, BIOS U30 05/24/2021
> [  376.909038] RIP: 0010:pmd_migration_entry_wait+0x132/0x140
> [  376.914562] Code: 02 00 00 00 5b 4c 89 c7 5d e9 8a e4 f6 ff 48 81 e2 00
> f0 ff ff 48 f7 d2 48 21 c2 89 d1 f7 c2 81 01 00 00 75 80 e9 44 ff ff ff
> <0f> 0b 48 8b 2d 75 bd 30 01 e9 ef fe ff ff 0f 1f 44 00 00 41 55 48
> [  376.933443] RSP: 0000:ffffb65a5e1cfdc8 EFLAGS: 00010246
> [  376.938701] RAX: 0017ffffc0000000 RBX: ffff908b8ecabaf8 RCX:
> ffffffffffffffff
> [  376.945878] RDX: 0000000000000000 RSI: ffff908b8ecabaf8 RDI:
> fffff497473b2ae8
> [  376.953055] RBP: fffff497473b2ae8 R08: fffff49747fa8080 R09:
> 0000000000000000
> [  376.960230] R10: 0000000000000000 R11: 0000000000000000 R12:
> 0000000000000af8
> [  376.967407] R13: 0400000000000000 R14: 0400000000000080 R15:
> ffff908bbef7b6a8
> [  376.974582] FS:  00007f5bb1f81700(0000) GS:ffff90e87fd80000(0000)
> knlGS:0000000000000000
> [  376.982718] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [  376.988497] CR2: 00007f5b2bfffd98 CR3: 00000001f793e006 CR4:
> 00000000007726e0
> [  376.995673] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
> 0000000000000000
> [  377.002849] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7:
> 0000000000000400
> [  377.010026] PKRU: 55555554
> [  377.012745] Call Trace:
> [  377.015207]  __handle_mm_fault+0x5ad/0x6e0
> [  377.019335]  handle_mm_fault+0xc5/0x290
> [  377.023194]  do_user_addr_fault+0x1cd/0x740
> [  377.027406]  exc_page_fault+0x54/0x110
> [  377.031182]  ? asm_exc_page_fault+0x8/0x30
> [  377.035307]  asm_exc_page_fault+0x1e/0x30
> [  377.039340] RIP: 0033:0x7f5bb91d6734
> [  377.042937] Code: 89 08 48 8b 35 dd 3b 21 00 4c 8d 0d d6 3b 21 00 31 c0
> 4c 39 ce 74 73 0f 1f 80 00 00 00 00 48 8d 96 40 fd ff ff 49 39 d2 74 22
> <48> 8b 96 d8 03 00 00 48 01 15 4e 7c 21 00 80 be 50 03 00 00 00 c7
> [  377.061820] RSP: 002b:00007f5bb1f7ff58 EFLAGS: 00010206
> [  377.067076] RAX: 0000000000000000 RBX: 0000000000000000 RCX:
> 00007f5ba0000020
> [  377.074255] RDX: 00007f5b2bfff700 RSI: 00007f5b2bfff9c0 RDI:
> 0000000000000001
> [  377.081429] RBP: 0000000000000001 R08: 0000000000000000 R09:
> 00007f5bb93ea2f0
> [  377.088606] R10: 00007f5bb1f81700 R11: 0000000000000202 R12:
> 0000000000000001
> [  377.095782] R13: 0000000000000006 R14: 0000000000000cb4 R15:
> 00007f5bb1f801f0
> [  377.102958] Modules linked in: ebt_arp(E) nft_meta_bridge(E)
> ip6_tables(E) xt_CT(E) nf_log_ipv4(E) nf_log_common(E) nft_limit(E)
> nft_counter(E) xt_LOG(E) xt_limit(E) xt_mac(E) xt_set(E) xt_multiport(E)
> xt_state(E) xt_conntrack(E) xt_comment(E) xt_physdev(E) nft_compat(E)
> ip_set_hash_net(E) ip_set(E) vhost_net(E) vhost(E) vhost_iotlb(E) tap(E)
> tun(E) tcp_diag(E) udp_diag(E) inet_diag(E) netconsole(E) nf_tables(E)
> vxlan(E) ip6_udp_tunnel(E) udp_tunnel(E) nfnetlink(E) binfmt_misc(E)
> iscsi_tcp(E) libiscsi_tcp(E) 8021q(E) garp(E) mrp(E) bonding(E) tls(E)
> vfat(E) fat(E) dm_service_time(E) dm_multipath(E) rpcrdma(E) sunrpc(E)
> rdma_ucm(E) ib_srpt(E) ib_isert(E) iscsi_target_mod(E) target_core_mod(E)
> ib_iser(E) rdma_cm(E) iw_cm(E) ib_cm(E) libiscsi(E) scsi_transport_iscsi(E)
> intel_rapl_msr(E) qedr(E) intel_rapl_common(E) ib_uverbs(E)
> isst_if_common(E) ib_core(E) nfit(E) libnvdimm(E) x86_pkg_temp_thermal(E)
> intel_powerclamp(E) coretemp(E) kvm_intel(E) kvm(E) irqbypass(E)
> crct10dif_pclmul(E)
> [  377.102999]  crc32_pclmul(E) ghash_clmulni_intel(E) rapl(E)
> intel_cstate(E) ipmi_ssif(E) acpi_ipmi(E) ipmi_si(E) mei_me(E) ioatdma(E)
> ipmi_devintf(E) dm_mod(E) ses(E) intel_uncore(E) pcspkr(E) qede(E)
> enclosure(E) tg3(E) mei(E) lpc_ich(E) hpilo(E) hpwdt(E)
> intel_pch_thermal(E) dca(E) ipmi_msghandler(E) acpi_power_meter(E) ext4(E)
> mbcache(E) jbd2(E) sd_mod(E) t10_pi(E) sg(E) qedf(E) qed(E) crc8(E)
> libfcoe(E) libfc(E) smartpqi(E) scsi_transport_fc(E) scsi_transport_sas(E)
> wmi(E) nf_conntrack(E) nf_defrag_ipv6(E) libcrc32c(E) crc32c_intel(E)
> nf_defrag_ipv4(E) br_netfilter(E) bridge(E) stp(E) llc(E)
> [  377.243468] ---[ end trace 04bce3bb051f7620 ]---
> [  377.385645] RIP: 0010:pmd_migration_entry_wait+0x132/0x140
> [  377.391194] Code: 02 00 00 00 5b 4c 89 c7 5d e9 8a e4 f6 ff 48 81 e2 00
> f0 ff ff 48 f7 d2 48 21 c2 89 d1 f7 c2 81 01 00 00 75 80 e9 44 ff ff ff
> <0f> 0b 48 8b 2d 75 bd 30 01 e9 ef fe ff ff 0f 1f 44 00 00 41 55 48
> [  377.410091] RSP: 0000:ffffb65a5e1cfdc8 EFLAGS: 00010246
> [  377.415355] RAX: 0017ffffc0000000 RBX: ffff908b8ecabaf8 RCX:
> ffffffffffffffff
> [  377.422540] RDX: 0000000000000000 RSI: ffff908b8ecabaf8 RDI:
> fffff497473b2ae8
> [  377.429721] RBP: fffff497473b2ae8 R08: fffff49747fa8080 R09:
> 0000000000000000
> [  377.436902] R10: 0000000000000000 R11: 0000000000000000 R12:
> 0000000000000af8
> [  377.444086] R13: 0400000000000000 R14: 0400000000000080 R15:
> ffff908bbef7b6a8
> [  377.451272] FS:  00007f5bb1f81700(0000) GS:ffff90e87fd80000(0000)
> knlGS:0000000000000000
> [  377.459415] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [  377.465196] CR2: 00007f5b2bfffd98 CR3: 00000001f793e006 CR4:
> 00000000007726e0
> [  377.472377] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
> 0000000000000000
> [  377.479556] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7:
> 0000000000000400
> [  377.486738] PKRU: 55555554
> [  377.489465] Kernel panic - not syncing: Fatal exception
> [  377.573911] Kernel Offset: 0xa000000 from 0xffffffff81000000 (relocation
> range: 0xffffffff80000000-0xffffffffbfffffff)
> [  377.716482] ---[ end Kernel panic - not syncing: Fatal exception ]---
>