Hi,
After commit ba168b52bf8e "mm: use rwsem assertion macros for
mmap_lock") was submitted, we started getting a lot of the
following warnings about a missing mmap write lock during VM boot:
------------[ cut here ]------------
WARNING: CPU: 1 PID: 58633 at include/linux/rwsem.h:85
track_pfn_remap+0x12b/0x130
Modules linked in: act_mirred act_skbedit vhost_vdpa cls_matchall
nfnetlink_cttimeout act_gact cls_flower sch_ingress mlx5_vdpa vringh vdpa
openvswitch nsh vhost_net vhost vhost_iotlb tap ip6table_mangle ip6table_nat
iptable_mangle nf_tables ip6table_filter ip6_tables xt_conntrack xt_MASQUERADE
nf_conntrack_netlink nfnetlink xt_addrtype iptable_nat nf_nat br_netfilter
rpcsec_gss_krb5 auth_rpcgss oid_registry overlay rpcrdma rdma_ucm ib_iser
libiscsi ib_umad scsi_transport_iscsi ib_ipoib rdma_cm iw_cm ib_cm mlx5_ib
ib_uverbs ib_core fuse mlx5_core
CPU: 1 PID: 58633 Comm: CPU 0/KVM Tainted: G W
6.10.0-rc1_for_upstream_min_debug_2024_05_29_17_06 #1
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
RIP: 0010:track_pfn_remap+0x12b/0x130
Code: 48 83 c4 08 b8 ea ff ff ff 5b 5d 41 5c 41 5d c3 48 83 c4 08 48 89 ef 48
89 f2 5b 31 c9 4c 89 c6 5d 41 5c 41 5d e9 f5 fb ff ff <0f> 0b eb 9b 90 0f 1f 44
00 00 80 3d ac 59 96 01 00 74 01 c3 48 89
RSP: 0018:ffff888350f8b8e0 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000001000 RCX: 0000000000000000
RDX: ffff8881080ca300 RSI: 0000000000001000 RDI: 0000000544003000
RBP: 0000000544003000 R08: ffff888106730a60 R09: 0000000000000000
R10: ffff888116eeff60 R11: 0000000000000000 R12: ffff888350f8b918
R13: ffff888149f99da8 R14: 0000000000001000 R15: 0000000000001000
FS: 00007f678d800700(0000) GS:ffff88852c880000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000004e54f8 CR3: 0000000112290004 CR4: 0000000000372eb0
Call Trace:
<TASK>
? __warn+0x78/0x110
? track_pfn_remap+0x12b/0x130
? report_bug+0x16d/0x180
? handle_bug+0x3c/0x60
? exc_invalid_op+0x14/0x70
? asm_exc_invalid_op+0x16/0x20
? track_pfn_remap+0x12b/0x130
remap_pfn_range+0x41/0xa0
vhost_vdpa_fault+0x6c/0xa0 [vhost_vdpa]
__do_fault+0x2f/0xb0
__handle_mm_fault+0x13d3/0x2210
handle_mm_fault+0xb0/0x260
fixup_user_fault+0x77/0x170
hva_to_pfn+0x2c5/0x4b0
kvm_faultin_pfn+0xd7/0x510
kvm_tdp_page_fault+0x111/0x190
kvm_mmu_do_page_fault+0x105/0x230
kvm_mmu_page_fault+0x7d/0x620
? vmx_deliver_interrupt+0x110/0x190
? __apic_accept_irq+0x16c/0x270
? vmx_vmexit+0x8d/0xc0
vmx_handle_exit+0x110/0x640
kvm_arch_vcpu_ioctl_run+0xdb0/0x1c20
kvm_vcpu_ioctl+0x263/0x6a0
? futex_wake+0x81/0x180
__x64_sys_ioctl+0x4a7/0x9d0
? __x64_sys_futex+0x73/0x1c0
? kvm_on_user_return+0x86/0x90
do_syscall_64+0x4c/0x100
entry_SYSCALL_64_after_hwframe+0x4b/0x53
RIP: 0033:0x7f679186a17b
Code: 0f 1e fa 48 8b 05 1d ad 0c 00 64 c7 00 26 00 00 00 48 c7 c0 ff ff ff ff
c3 66 0f 1f 44 00 00 f3 0f 1e fa b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01
c3 48 8b 0d ed ac 0c 00 f7 d8 64 89 01 48
RSP: 002b:00007f678d7ff788 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 000000000000ae80 RCX: 00007f679186a17b
RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 0000000000000059
RBP: 000055da5ee22050 R08: 000055da44b28160 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000000000
R13: 000055da452b05e0 R14: 0000000000000001 R15: 0000000000000000
</TASK>
---[ end trace 0000000000000000 ]---
The warnings show up only when the vdpa page-per-vq option is used (doorbell
mapping to guest).
The issue seems to have existed before, but was visible only with CONFIG_LOCKDEP
enabled. I tried finding if this was introduced in more recent kernels, but
stopped after going as far back as 6.5: the issue was still visible there.
The warning is triggered for the following call chain:
vhost_vdpa_fault()
-> remap_pfn_range()
-> remap_pfn_range_notrack()
-> vm_flags_set()
-> vma_start_write()
-> __is_vma_write_locked()
-> mmap_assert_write_locked()
I've been trying to follow how the mm write lock is dropped in the above call
chain or not taken at all. But I couldn't make much sense of it...
Any ideas of what could have gone wrong here?
Thanks,
Dragos
