Kernel NULL pointer deref and data corruptions with xfs on 6.1

From: Daniel Dao
Date: Fri Jul 21 2023 - 06:49:29 EST

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Hi,

In the past, we reported some corruptions on xfs/iomap/xarray combinations on
kernel 6.1. This happened very rarely ( once a week for every 10000 hosts), and
the host exhibited symptoms such as: rcu_preempt self-detected stalls,
NULL pointer
dereferences or deadlock when reading a particular file.

We do not have a reproducer yet, but we now have more debugging data
which hopefully
should help narrow this down. Details as followed:

1. Kernel NULL pointer deferencences in __filemap_get_folio

This happened on a few different hosts, with a few different repeated addresses.
The addresses are 0000000000000036, 0000000000000076,
00000000000000f6. This looks
like the xarray is corrupted and we were trying to do some work on a
sibling entry.

BUG: kernel NULL pointer dereference, address: 0000000000000036
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 18806c5067 P4D 18806c5067 PUD 188ed48067 PMD 0
Oops: 0000 [#1] PREEMPT SMP NOPTI
CPU: 73 PID: 3579408 Comm: prometheus Tainted: G O
6.1.34-cloudflare-2023.6.7 #1
Hardware name: GIGABYTE R162-Z12-CD1/MZ12-HD4-CD, BIOS M03 11/19/2021
RIP: 0010:__filemap_get_folio (arch/x86/include/asm/atomic.h:29
include/linux/atomic/atomic-arch-fallback.h:1242
include/linux/atomic/atomic-arch-fallback.h:1267
include/linux/atomic/atomic-instrumented.h:608
include/linux/page_ref.h:238 include/linux/page_ref.h:247
include/linux/page_ref.h:280 include/linux/page_ref.h:313
mm/filemap.c:1863 mm/filemap.c:1915)
Code: 10 e8 99 ac 84 00 48 3d 06 04 00 00 49 89 c4 74 e2 48 3d 02
04 00 00 74 da 48 85 c0 0f 84 2e 02 00 00 a8 01 0f 85 e3 00 00 00 <8b>
40 34 85 c0 74 c2 8d 50 01 4d 8d 7c 24 34 f0 41 0f b1 54 24 34
All code
========
0: 10 e8 adc %ch,%al
2: 99 cltd
3: ac lods %ds:(%rsi),%al
4: 84 00 test %al,(%rax)
6: 48 3d 06 04 00 00 cmp $0x406,%rax
c: 49 89 c4 mov %rax,%r12
f: 74 e2 je 0xfffffffffffffff3
11: 48 3d 02 04 00 00 cmp $0x402,%rax
17: 74 da je 0xfffffffffffffff3
19: 48 85 c0 test %rax,%rax
1c: 0f 84 2e 02 00 00 je 0x250
22: a8 01 test $0x1,%al
24: 0f 85 e3 00 00 00 jne 0x10d
2a:* 8b 40 34 mov 0x34(%rax),%eax <-- trapping instruction
2d: 85 c0 test %eax,%eax
2f: 74 c2 je 0xfffffffffffffff3
31: 8d 50 01 lea 0x1(%rax),%edx
34: 4d 8d 7c 24 34 lea 0x34(%r12),%r15
39: f0 41 0f b1 54 24 34 lock cmpxchg %edx,0x34(%r12)

Code starting with the faulting instruction
===========================================
0: 8b 40 34 mov 0x34(%rax),%eax
3: 85 c0 test %eax,%eax
5: 74 c2 je 0xffffffffffffffc9
7: 8d 50 01 lea 0x1(%rax),%edx
a: 4d 8d 7c 24 34 lea 0x34(%r12),%r15
f: f0 41 0f b1 54 24 34 lock cmpxchg %edx,0x34(%r12)
RSP: 0000:ffffaf5587cdfc60 EFLAGS: 00010246
RAX: 0000000000000002 RBX: 0000000000000000 RCX: 0000000000000002
RDX: 0000000000000008 RSI: ffffa45181fa8000 RDI: ffffaf5587cdfc70
RBP: 0000000000000000 R08: 0000000000000402 R09: 000000000006e44f
R10: 000000000006e450 R11: 000000000006e448 R12: 0000000000000002
R13: ffffa3fff6fdfeb0 R14: 000000000006e44a R15: 00000000000000d1
FS: 000000c9e385ac90(0000) GS:ffffa4153fc40000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000036 CR3: 000000296a1bc002 CR4: 0000000000770ee0
PKRU: 55555554
Call Trace:
<TASK>
? __die_body.cold (arch/x86/kernel/dumpstack.c:478
arch/x86/kernel/dumpstack.c:465 arch/x86/kernel/dumpstack.c:420)
? page_fault_oops (arch/x86/mm/fault.c:727)
? migrate_task_rq_fair (include/linux/sched.h:1921
kernel/sched/fair.c:3932 kernel/sched/fair.c:7497)
? do_user_addr_fault (include/linux/kprobes.h:404
include/linux/kprobes.h:597 arch/x86/mm/fault.c:1280)
? ttwu_queue_wakelist (kernel/sched/core.c:3880)
? exc_page_fault (arch/x86/include/asm/irqflags.h:40
arch/x86/include/asm/irqflags.h:75 arch/x86/mm/fault.c:1527
arch/x86/mm/fault.c:1575)
? asm_exc_page_fault (arch/x86/include/asm/idtentry.h:570)
? __filemap_get_folio (arch/x86/include/asm/atomic.h:29
include/linux/atomic/atomic-arch-fallback.h:1242
include/linux/atomic/atomic-arch-fallback.h:1267
include/linux/atomic/atomic-instrumented.h:608
include/linux/page_ref.h:238 include/linux/page_ref.h:247
include/linux/page_ref.h:280 include/linux/page_ref.h:313
mm/filemap.c:1863 mm/filemap.c:1915)
filemap_fault (mm/filemap.c:3120)
? preempt_count_add (include/linux/ftrace.h:950
kernel/sched/core.c:5685 kernel/sched/core.c:5682
kernel/sched/core.c:5710)
__do_fault (mm/memory.c:4234)
do_fault (mm/memory.c:4564 mm/memory.c:4692)
__handle_mm_fault (mm/memory.c:4964 mm/memory.c:5106)
handle_mm_fault (mm/memory.c:5227)
do_user_addr_fault (include/linux/sched/signal.h:433
arch/x86/mm/fault.c:1430)
exc_page_fault (arch/x86/include/asm/irqflags.h:40
arch/x86/include/asm/irqflags.h:75 arch/x86/mm/fault.c:1527
arch/x86/mm/fault.c:1575)
asm_exc_page_fault (arch/x86/include/asm/idtentry.h:570)
RIP: 0033:0x268b8b9
Code: 70 48 89 4c 24 78 48 8b 94 24 b8 00 00 00 0f 1f 00 48 85 d2
74 3f 48 89 ce 48 29 d9 4c 8d 49 04 49 f7 d9 49 c1 f9 3f 49 21 f9 <46>
8b 0c 08 44 89 4c 24 34 90 90 48 89 d3 48 89 c1 41 b8 01 00 00
All code
========
0: 70 48 jo 0x4a
2: 89 4c 24 78 mov %ecx,0x78(%rsp)
6: 48 8b 94 24 b8 00 00 mov 0xb8(%rsp),%rdx
d: 00
e: 0f 1f 00 nopl (%rax)
11: 48 85 d2 test %rdx,%rdx
14: 74 3f je 0x55
16: 48 89 ce mov %rcx,%rsi
19: 48 29 d9 sub %rbx,%rcx
1c: 4c 8d 49 04 lea 0x4(%rcx),%r9
20: 49 f7 d9 neg %r9
23: 49 c1 f9 3f sar $0x3f,%r9
27: 49 21 f9 and %rdi,%r9
2a:* 46 8b 0c 08 mov (%rax,%r9,1),%r9d <-- trapping
instruction
2e: 44 89 4c 24 34 mov %r9d,0x34(%rsp)
33: 90 nop
34: 90 nop
35: 48 89 d3 mov %rdx,%rbx
38: 48 89 c1 mov %rax,%rcx
3b: 41 rex.B
3c: b8 .byte 0xb8
3d: 01 00 add %eax,(%rax)
...

Code starting with the faulting instruction
===========================================
0: 46 8b 0c 08 mov (%rax,%r9,1),%r9d
4: 44 89 4c 24 34 mov %r9d,0x34(%rsp)
9: 90 nop
a: 90 nop
b: 48 89 d3 mov %rdx,%rbx
e: 48 89 c1 mov %rax,%rcx
11: 41 rex.B
12: b8 .byte 0xb8
13: 01 00 add %eax,(%rax)
...
RSP: 002b:000000cbc509f520 EFLAGS: 00010202
RAX: 00007e81cf427e0c RBX: 00000000000222cc RCX: 00000000123817b2
RDX: 000000c00001ac00 RSI: 00000000123a3a7e RDI: 00000000000222c8
RBP: 000000cbc509f5b0 R08: 0000000003cb5910 R09: 00000000000222c8
R10: 000000c4de3dea00 R11: 0000000000000123 R12: 0000000000000000
R13: 0000000000000005 R14: 000000c83bad2340 R15: 0000010000000000
</TASK>
Modules linked in: xt_connlabel xt_MASQUERADE nf_conntrack_netlink
xfrm_user xfrm_algo xt_addrtype br_netfilter bridge overlay zstd
zstd_compress zram zsmalloc tun tcp_diag inet_diag raid0 md_mod essiv
dm_crypt trusted asn1_encoder tee ip6table_filter ip6table_mangle
ip6table_raw ip6table_security ip6table_nat ip6_tables xt_bpf
xt_conntrack xt_multiport xt_set iptable_filter xt_NFLOG nfnetlink_log
xt_connbytes xt_comment xt_connmark xt_statistic iptable_mangle xt_nat
xt_tcpudp iptable_nat nf_nat xt_CT iptable_raw ip_set_hash_ip
ip_set_hash_net ip_set nfnetlink sch_fq nf_conntrack nf_defrag_ipv6
nf_defrag_ipv4 8021q garp mrp stp llc bonding nvme_fabrics amd64_edac
kvm_amd ipmi_ssif kvm irqbypass crc32_pclmul crc32c_intel sha512_ssse3
acpi_ipmi mlx5_core aesni_intel ipmi_si mlxfw rapl xhci_pci nvme tls
ipmi_devintf tiny_power_button psample nvme_core xhci_hcd i2c_piix4
ccp ipmi_msghandler button fuse dm_mod dax efivarfs ip_tables x_tables
bcmcrypt(O)
crypto_simd cryptd
CR2: 0000000000000036
---[ end trace 0000000000000000 ]---
RIP: 0010:__filemap_get_folio (arch/x86/include/asm/atomic.h:29
include/linux/atomic/atomic-arch-fallback.h:1242
include/linux/atomic/atomic-arch-fallback.h:1267
include/linux/atomic/atomic-instrumented.h:608
include/linux/page_ref.h:238 include/linux/page_ref.h:247
include/linux/page_ref.h:280 include/linux/page_ref.h:313
mm/filemap.c:1863 mm/filemap.c:1915)
Code: 10 e8 99 ac 84 00 48 3d 06 04 00 00 49 89 c4 74 e2 48 3d 02
04 00 00 74 da 48 85 c0 0f 84 2e 02 00 00 a8 01 0f 85 e3 00 00 00 <8b>
40 34 85 c0 74 c2 8d 50 01 4d 8d 7c 24 34 f0 41 0f b1 54 24 34
All code
========
0: 10 e8 adc %ch,%al
2: 99 cltd
3: ac lods %ds:(%rsi),%al
4: 84 00 test %al,(%rax)
6: 48 3d 06 04 00 00 cmp $0x406,%rax
c: 49 89 c4 mov %rax,%r12
f: 74 e2 je 0xfffffffffffffff3
11: 48 3d 02 04 00 00 cmp $0x402,%rax
17: 74 da je 0xfffffffffffffff3
19: 48 85 c0 test %rax,%rax
1c: 0f 84 2e 02 00 00 je 0x250
22: a8 01 test $0x1,%al
24: 0f 85 e3 00 00 00 jne 0x10d
2a:* 8b 40 34 mov 0x34(%rax),%eax <-- trapping instruction
2d: 85 c0 test %eax,%eax
2f: 74 c2 je 0xfffffffffffffff3
31: 8d 50 01 lea 0x1(%rax),%edx
34: 4d 8d 7c 24 34 lea 0x34(%r12),%r15
39: f0 41 0f b1 54 24 34 lock cmpxchg %edx,0x34(%r12)

Code starting with the faulting instruction
===========================================
0: 8b 40 34 mov 0x34(%rax),%eax
3: 85 c0 test %eax,%eax
5: 74 c2 je 0xffffffffffffffc9
7: 8d 50 01 lea 0x1(%rax),%edx
a: 4d 8d 7c 24 34 lea 0x34(%r12),%r15
f: f0 41 0f b1 54 24 34 lock cmpxchg %edx,0x34(%r12)
RSP: 0000:ffffaf5587cdfc60 EFLAGS: 00010246
RAX: 0000000000000002 RBX: 0000000000000000 RCX: 0000000000000002
RDX: 0000000000000008 RSI: ffffa45181fa8000 RDI: ffffaf5587cdfc70
RBP: 0000000000000000 R08: 0000000000000402 R09: 000000000006e44f
R10: 000000000006e450 R11: 000000000006e448 R12: 0000000000000002
R13: ffffa3fff6fdfeb0 R14: 000000000006e44a R15: 00000000000000d1
FS: 000000c9e385ac90(0000) GS:ffffa4153fc40000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000036 CR3: 000000296a1bc002 CR4: 0000000000770ee0
PKRU: 55555554

BUG: kernel NULL pointer dereference, address: 0000000000000076
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 7acd78067 P4D 7acd78067 PUD 7acd79067 PMD 0
Oops: 0000 [#1] PREEMPT SMP NOPTI
CPU: 93 PID: 3784417 Comm: prometheus Tainted: G O
6.1.20-cloudflare-2023.3.18 #1
Hardware name: GIGABYTE R162-Z13-CD/MZ12-HD2-CD, BIOS R13 07/17/2020
RIP: 0010:__filemap_get_folio (arch/x86/include/asm/atomic.h:29
include/linux/atomic/atomic-arch-fallback.h:1242
include/linux/atomic/atomic-arch-fallback.h:1267
include/linux/atomic/atomic-instrumented.h:608
include/linux/page_ref.h:238 include/linux/page_ref.h:247
include/linux/page_ref.h:280 include/linux/page_ref.h:313
mm/filemap.c:1863 mm/filemap.c:1915)
Code: 10 e8 b9 a4 84 00 48 3d 06 04 00 00 49 89 c4 74 e2 48 3d 02
04 00 00 74 da 48 85 c0 0f 84 2e 02 00 00 a8 01 0f 85 e3 00 00 00 <8b>
40 34 85 c0 74 c2 8d 50 01 4d 8d 7c 24 34 f0 41 0f b1 54 24 34
All code
========
0: 10 e8 adc %ch,%al
2: b9 a4 84 00 48 mov $0x480084a4,%ecx
7: 3d 06 04 00 00 cmp $0x406,%eax
c: 49 89 c4 mov %rax,%r12
f: 74 e2 je 0xfffffffffffffff3
11: 48 3d 02 04 00 00 cmp $0x402,%rax
17: 74 da je 0xfffffffffffffff3
19: 48 85 c0 test %rax,%rax
1c: 0f 84 2e 02 00 00 je 0x250
22: a8 01 test $0x1,%al
24: 0f 85 e3 00 00 00 jne 0x10d
2a:* 8b 40 34 mov 0x34(%rax),%eax <-- trapping instruction
2d: 85 c0 test %eax,%eax
2f: 74 c2 je 0xfffffffffffffff3
31: 8d 50 01 lea 0x1(%rax),%edx
34: 4d 8d 7c 24 34 lea 0x34(%r12),%r15
39: f0 41 0f b1 54 24 34 lock cmpxchg %edx,0x34(%r12)

Code starting with the faulting instruction
===========================================
0: 8b 40 34 mov 0x34(%rax),%eax
3: 85 c0 test %eax,%eax
5: 74 c2 je 0xffffffffffffffc9
7: 8d 50 01 lea 0x1(%rax),%edx
a: 4d 8d 7c 24 34 lea 0x34(%r12),%r15
f: f0 41 0f b1 54 24 34 lock cmpxchg %edx,0x34(%r12)
RSP: 0000:ffffb15106683c60 EFLAGS: 00010246
RAX: 0000000000000042 RBX: 0000000000000000 RCX: 0000000000000002
RDX: 0000000000000018 RSI: ffff934b0029efc8 RDI: ffffb15106683c70
RBP: 0000000000000000 R08: 0000000000000402 R09: 00000000000cbe5f
R10: 00000000000cbe60 R11: 00000000000cbe5c R12: 0000000000000042
R13: ffff93449c251eb0 R14: 00000000000cbe59 R15: 00000000000000d1
FS: 000000c000300090(0000) GS:ffff937e6ed40000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000076 CR3: 0000000a6528e000 CR4: 0000000000350ee0
Call Trace:
<TASK>
filemap_fault (mm/filemap.c:3120)
? preempt_count_add (include/linux/ftrace.h:950
kernel/sched/core.c:5685 kernel/sched/core.c:5682
kernel/sched/core.c:5710)
__do_fault (mm/memory.c:4234)
do_fault (mm/memory.c:4564 mm/memory.c:4692)
__handle_mm_fault (mm/memory.c:4964 mm/memory.c:5106)
handle_mm_fault (mm/memory.c:5227)
do_user_addr_fault (include/linux/sched/signal.h:433
arch/x86/mm/fault.c:1430)
exc_page_fault (arch/x86/include/asm/irqflags.h:40
arch/x86/include/asm/irqflags.h:75 arch/x86/mm/fault.c:1527
arch/x86/mm/fault.c:1575)
asm_exc_page_fault (arch/x86/include/asm/idtentry.h:570)
RIP: 0033:0x268b8b9
Code: 70 48 89 4c 24 78 48 8b 94 24 b8 00 00 00 0f 1f 00 48 85 d2
74 3f 48 89 ce 48 29 d9 4c 8d 49 04 49 f7 d9 49 c1 f9 3f 49 21 f9 <46>
8b 0c 08 44 89 4c 24 34 90 90 48 89 d3 48 89 c1 41 b8 01 00 00
All code
========
0: 70 48 jo 0x4a
2: 89 4c 24 78 mov %ecx,0x78(%rsp)
6: 48 8b 94 24 b8 00 00 mov 0xb8(%rsp),%rdx
d: 00
e: 0f 1f 00 nopl (%rax)
11: 48 85 d2 test %rdx,%rdx
14: 74 3f je 0x55
16: 48 89 ce mov %rcx,%rsi
19: 48 29 d9 sub %rbx,%rcx
1c: 4c 8d 49 04 lea 0x4(%rcx),%r9
20: 49 f7 d9 neg %r9
23: 49 c1 f9 3f sar $0x3f,%r9
27: 49 21 f9 and %rdi,%r9
2a:* 46 8b 0c 08 mov (%rax,%r9,1),%r9d <-- trapping
instruction
2e: 44 89 4c 24 34 mov %r9d,0x34(%rsp)
33: 90 nop
34: 90 nop
35: 48 89 d3 mov %rdx,%rbx
38: 48 89 c1 mov %rax,%rcx
3b: 41 rex.B
3c: b8 .byte 0xb8
3d: 01 00 add %eax,(%rax)
...

Code starting with the faulting instruction
===========================================
0: 46 8b 0c 08 mov (%rax,%r9,1),%r9d
4: 44 89 4c 24 34 mov %r9d,0x34(%rsp)
9: 90 nop
a: 90 nop
b: 48 89 d3 mov %rdx,%rbx
e: 48 89 c1 mov %rax,%rcx
11: 41 rex.B
12: b8 .byte 0xb8
13: 01 00 add %eax,(%rax)
...
RSP: 002b:000000d735bb3558 EFLAGS: 00010206
RAX: 00007c018402dad8 RBX: 000000000002c3d8 RCX: 0000000037f9be1c
RDX: 000000c000222c00 RSI: 0000000037fc81f4 RDI: 000000000002c3d4
RBP: 000000d735bb35e8 R08: 0000000003cb5910 R09: 000000000002c3d4
R10: 000000c385d2a000 R11: 0000000000000021 R12: 0000000000000000
R13: 000000000000000b R14: 000000d1bb70e340 R15: 0000000001000000
</TASK>
Modules linked in: veth xt_MASQUERADE nf_conntrack_netlink
xfrm_user xfrm_algo xt_addrtype br_netfilter bridge overlay raid1
md_mod essiv dm_crypt trusted tee asn1_encoder xt_hl ip6table_filter
ip6table_mangle ip6table_raw ip6table_security ip6table_nat ip6_tables
xt_tcpudp xt_conntrack xt_comment xt_multiport xt_set iptable_filter
iptable_mangle iptable_nat nf_nat xt_CT iptable_raw ip_set_hash_ip
ip_set_hash_net ip_set nfnetlink tcp_bbr sch_fq nf_conntrack
nf_defrag_ipv6 nf_defrag_ipv4 8021q mrp garp stp llc bonding
amd64_edac kvm_amd ipmi_ssif kvm irqbypass crc32_pclmul crc32c_intel
mlx5_core sha512_ssse3 psample acpi_ipmi aesni_intel xhci_pci nvme
ipmi_si rapl tls ipmi_devintf tiny_power_button nvme_core mlxfw
xhci_hcd i2c_piix4 ccp ipmi_msghandler button fuse dm_mod dax efivarfs
ip_tables x_tables bcmcrypt(O) crypto_simd cryptd
CR2: 0000000000000076
---[ end trace 0000000000000000 ]---
RIP: 0010:__filemap_get_folio (arch/x86/include/asm/atomic.h:29
include/linux/atomic/atomic-arch-fallback.h:1242
include/linux/atomic/atomic-arch-fallback.h:1267
include/linux/atomic/atomic-instrumented.h:608
include/linux/page_ref.h:238 include/linux/page_ref.h:247
include/linux/page_ref.h:280 include/linux/page_ref.h:313
mm/filemap.c:1863 mm/filemap.c:1915)
Code: 10 e8 b9 a4 84 00 48 3d 06 04 00 00 49 89 c4 74 e2 48 3d 02
04 00 00 74 da 48 85 c0 0f 84 2e 02 00 00 a8 01 0f 85 e3 00 00 00 <8b>
40 34 85 c0 74 c2 8d 50 01 4d 8d 7c 24 34 f0 41 0f b1 54 24 34
All code
========
0: 10 e8 adc %ch,%al
2: b9 a4 84 00 48 mov $0x480084a4,%ecx
7: 3d 06 04 00 00 cmp $0x406,%eax
c: 49 89 c4 mov %rax,%r12
f: 74 e2 je 0xfffffffffffffff3
11: 48 3d 02 04 00 00 cmp $0x402,%rax
17: 74 da je 0xfffffffffffffff3
19: 48 85 c0 test %rax,%rax
1c: 0f 84 2e 02 00 00 je 0x250
22: a8 01 test $0x1,%al
24: 0f 85 e3 00 00 00 jne 0x10d
2a:* 8b 40 34 mov 0x34(%rax),%eax <-- trapping instruction
2d: 85 c0 test %eax,%eax
2f: 74 c2 je 0xfffffffffffffff3
31: 8d 50 01 lea 0x1(%rax),%edx
34: 4d 8d 7c 24 34 lea 0x34(%r12),%r15
39: f0 41 0f b1 54 24 34 lock cmpxchg %edx,0x34(%r12)

Code starting with the faulting instruction
===========================================
0: 8b 40 34 mov 0x34(%rax),%eax
3: 85 c0 test %eax,%eax
5: 74 c2 je 0xffffffffffffffc9
7: 8d 50 01 lea 0x1(%rax),%edx
a: 4d 8d 7c 24 34 lea 0x34(%r12),%r15
f: f0 41 0f b1 54 24 34 lock cmpxchg %edx,0x34(%r12)
RSP: 0000:ffffb15106683c60 EFLAGS: 00010246
RAX: 0000000000000042 RBX: 0000000000000000 RCX: 0000000000000002
RDX: 0000000000000018 RSI: ffff934b0029efc8 RDI: ffffb15106683c70
RBP: 0000000000000000 R08: 0000000000000402 R09: 00000000000cbe5f
R10: 00000000000cbe60 R11: 00000000000cbe5c R12: 0000000000000042
R13: ffff93449c251eb0 R14: 00000000000cbe59 R15: 00000000000000d1
FS: 000000c000300090(0000) GS:ffff937e6ed40000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000076 CR3: 0000000a6528e000 CR4: 0000000000350ee0
note: prometheus[3784417] exited with irqs disabled

2. Kernel NULL pointer deferencences in xfs_read_iomap_begin

BUG: unable to handle page fault for address: 0000000000034668
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 11cfd37067 P4D 11cfd37067 PUD b88086067 PMD 0
Oops: 0000 [#1] PREEMPT SMP NOPTI
CPU: 124 PID: 3831226 Comm: rocksdb:low Kdump: loaded Tainted: G
W O L 6.1.27-cloudflare-2023.5.0 #1
Hardware name: HYVE EDGE-METAL-GEN11/HS1811D_Lite, BIOS V0.11-sig 12/23/2022
RIP: 0010:xfs_read_iomap_begin (fs/xfs/xfs_iomap.c:1200)
Code: 0f 1f 44 00 00 41 57 41 56 41 55 41 54 55 53 48 83 ec 50 48
89 14 24 4c 89 44 24 08 65 48 8b 04 25 28 00 00 00 48 89 44 24 48 <48>
8b 87 >
All code
========
0: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
5: 41 57 push %r15
7: 41 56 push %r14
9: 41 55 push %r13
b: 41 54 push %r12
d: 55 push %rbp
e: 53 push %rbx
f: 48 83 ec 50 sub $0x50,%rsp
13: 48 89 14 24 mov %rdx,(%rsp)
17: 4c 89 44 24 08 mov %r8,0x8(%rsp)
1c: 65 48 8b 04 25 28 00 mov %gs:0x28,%rax
23: 00 00
25: 48 89 44 24 48 mov %rax,0x48(%rsp)
2a:* 48 rex.W <-- trapping instruction
2b: 8b .byte 0x8b
2c: 87 00 xchg %eax,(%rax)

Code starting with the faulting instruction
===========================================
0: 48 rex.W
1: 8b .byte 0x8b
2: 87 00 xchg %eax,(%rax)
RSP: 0018:ffffa63810733a70 EFLAGS: 00010282
RAX: 78ac714f0997e100 RBX: ffffa63810733b40 RCX: 0000000000000000
RDX: 0000000000004000 RSI: 0000000000000000 RDI: 00000000000347a0
RBP: ffffffff8664d950 R08: ffffa63810733b68 R09: ffffa63810733bb0
R10: 000000000001f627 R11: 0000000000000000 R12: ffffa63810733b68
R13: ffffa63810733bb0 R14: 00000000000019c1 R15: 00000000fffffff5
FS: 00007f48d8504700(0000) GS:ffffa2fe5ef00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000034668 CR3: 00000013037ec001 CR4: 0000000000770ee0
PKRU: 55555554
Call Trace:
<TASK>
? __mod_memcg_lruvec_state (mm/memcontrol.c:613 mm/memcontrol.c:799)
iomap_iter (fs/iomap/iter.c:76)
iomap_read_folio (fs/iomap/buffered-io.c:342)
? xfs_end_bio (fs/xfs/xfs_aops.c:542)
filemap_read_folio (mm/filemap.c:2407)
filemap_get_pages (mm/filemap.c:2492 mm/filemap.c:2606)
filemap_read (mm/filemap.c:2677)
xfs_file_buffered_read (fs/xfs/xfs_file.c:278)
xfs_file_read_iter (fs/xfs/xfs_file.c:304)
vfs_read (fs/read_write.c:390 fs/read_write.c:470)
__x64_sys_pread64 (include/linux/file.h:44 fs/read_write.c:666
fs/read_write.c:675 fs/read_write.c:672 fs/read_write.c:672)
do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80)
entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:120)
RIP: 0033:0x7f49061ca917
Code: 08 89 3c 24 48 89 4c 24 18 e8 05 f4 ff ff 4c 8b 54 24 18 48
8b 54 24 10 41 89 c0 48 8b 74 24 08 8b 3c 24 b8 11 00 00 00 0f 05 <48>
3d 00 >
All code
========
0: 08 89 3c 24 48 89 or %cl,-0x76b7dbc4(%rcx)
6: 4c 24 18 rex.WR and $0x18,%al
9: e8 05 f4 ff ff call 0xfffffffffffff413
e: 4c 8b 54 24 18 mov 0x18(%rsp),%r10
13: 48 8b 54 24 10 mov 0x10(%rsp),%rdx
18: 41 89 c0 mov %eax,%r8d
1b: 48 8b 74 24 08 mov 0x8(%rsp),%rsi
20: 8b 3c 24 mov (%rsp),%edi
23: b8 11 00 00 00 mov $0x11,%eax
28: 0f 05 syscall
2a:* 48 rex.W <-- trapping instruction
2b: 3d .byte 0x3d
...

Code starting with the faulting instruction
===========================================
0: 48 rex.W
1: 3d .byte 0x3d
...
RSP: 002b:00007f48d84ffc70 EFLAGS: 00000293 ORIG_RAX: 0000000000000011
RAX: ffffffffffffffda RBX: 00000000018a0c90 RCX: 00007f49061ca917
RDX: 00000000000c294f RSI: 000000002265e000 RDI: 000000000000003c
RBP: 00007f48d84ffda0 R08: 0000000000000000 R09: 00007f48d84ffe60
R10: 000000000191dcd8 R11: 0000000000000293 R12: 0000000007c3c6c0
R13: 00000000000c294f R14: 00000000000c294f R15: 000000000191dcd8
</TASK>
Modules linked in: xt_connlabel overlay nft_compat esp4
xt_hashlimit ip_set_hash_netport xt_length nf_conntrack_netlink
mpls_gso mpls_iptunnel >
tcp_bbr sch_fq nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 8021q
garp mrp stp llc ipmi_ssif amd64_edac kvm_amd kvm irqbypass
crc32_pclmul crc32>
CR2: 0000000000034668
---[ end trace 0000000000000000 ]---

We also have a deadlock reading a very specific file on this host. We managed to
do a kdump on this host and extracted out the state of the mapping.

>>> trace
#0 context_switch (/cfsetup_build/build/linux/kernel/sched/core.c:5241:2)
#1 __schedule (/cfsetup_build/build/linux/kernel/sched/core.c:6554:8)
#2 schedule (/cfsetup_build/build/linux/kernel/sched/core.c:6630:3)
#3 io_schedule (/cfsetup_build/build/linux/kernel/sched/core.c:8774:2)
#4 folio_wait_bit_common (/cfsetup_build/build/linux/mm/filemap.c:1296:4)
#5 folio_put_wait_locked (/cfsetup_build/build/linux/mm/filemap.c:1465:9)
#6 filemap_update_page (/cfsetup_build/build/linux/mm/filemap.c:2472:4)
#7 filemap_get_pages (/cfsetup_build/build/linux/mm/filemap.c:2606:9)
#8 filemap_read (/cfsetup_build/build/linux/mm/filemap.c:2676:11)
#9 xfs_file_buffered_read
(/cfsetup_build/build/linux/fs/xfs/xfs_file.c:277:8)
#10 xfs_file_read_iter (/cfsetup_build/build/linux/fs/xfs/xfs_file.c:302:9)
#11 call_read_iter (/cfsetup_build/build/linux/include/linux/fs.h:2199:9)
#12 new_sync_read (/cfsetup_build/build/linux/fs/read_write.c:389:8)
#13 vfs_read (/cfsetup_build/build/linux/fs/read_write.c:470:9)
#14 ksys_read (/cfsetup_build/build/linux/fs/read_write.c:613:9)
#15 do_syscall_x64
(/cfsetup_build/build/linux/arch/x86/entry/common.c:50:14)
#16 do_syscall_64 (/cfsetup_build/build/linux/arch/x86/entry/common.c:80:7)
#17 entry_SYSCALL_64+0x83/0x164
(/cfsetup_build/build/linux/arch/x86/entry/entry_64.S:120)
#18 0x7f05f0b093ce
>>> folio = trace[6]['folio']
>>> decode_page_flags(folio)
'PG_locked|PG_waiters|PG_head'
>>> folio
*(struct folio *)0xffffd67406346000 = {
.flags = (unsigned long)13510764522438785,
.lru = (struct list_head){
.next = (struct list_head *)0xdead000000000100,
.prev = (struct list_head *)0xdead000000000122,
},
.__filler = (void *)0xdead000000000100,
.mlock_count = (unsigned int)290,
.mapping = (struct address_space *)0x0,
.index = (unsigned long)18446641474676726016,
.private = (void *)0x400000,
._mapcount = (atomic_t){
.counter = (int)-1,
},
._refcount = (atomic_t){
.counter = (int)1,
},
.memcg_data = (unsigned long)0,
.page = (struct page){
.flags = (unsigned long)13510764522438785,
.lru = (struct list_head){
.next = (struct list_head *)0xdead000000000100,
.prev = (struct list_head *)0xdead000000000122,
},
.__filler = (void *)0xdead000000000100,
.mlock_count = (unsigned int)290,
.buddy_list = (struct list_head){
.next = (struct list_head *)0xdead000000000100,
.prev = (struct list_head *)0xdead000000000122,
},
.pcp_list = (struct list_head){
.next = (struct list_head *)0xdead000000000100,
.prev = (struct list_head *)0xdead000000000122,
},
.mapping = (struct address_space *)0x0,
.index = (unsigned long)18446641474676726016,
.private = (unsigned long)4194304,
.pp_magic = (unsigned long)16045481047390945536,
.pp = (struct page_pool *)0xdead000000000122,
._pp_mapping_pad = (unsigned long)0,
.dma_addr = (unsigned long)18446641474676726016,
.dma_addr_upper = (unsigned long)4194304,
.pp_frag_count = (atomic_long_t){
.counter = (s64)4194304,
},
.compound_head = (unsigned long)16045481047390945536,
.compound_dtor = (unsigned char)34,
.compound_order = (unsigned char)1,
.compound_mapcount = (atomic_t){
.counter = (int)-559087616,
},
.compound_pincount = (atomic_t){
.counter = (int)0,
},
.compound_nr = (unsigned int)0,
._compound_pad_1 = (unsigned long)16045481047390945536,
._compound_pad_2 = (unsigned long)16045481047390945570,
.deferred_list = (struct list_head){
.next = (struct list_head *)0x0,
.prev = (struct list_head *)0xffffa2afcd181900,
},
._pt_pad_1 = (unsigned long)16045481047390945536,
.pmd_huge_pte = (pgtable_t)0xdead000000000122,
._pt_pad_2 = (unsigned long)0,
.pt_mm = (struct mm_struct *)0xffffa2afcd181900,
.pt_frag_refcount = (atomic_t){
.counter = (int)-854058752,
},
.ptl = (spinlock_t){
.rlock = (struct raw_spinlock){
.raw_lock = (arch_spinlock_t){
.val = (atomic_t){
.counter = (int)4194304,
},
.locked = (u8)0,
.pending = (u8)0,
.locked_pending = (u16)0,
.tail = (u16)64,
},
},
},
.pgmap = (struct dev_pagemap *)0xdead000000000100,
.zone_device_data = (void *)0xdead000000000122,
.callback_head = (struct callback_head){
.next = (struct callback_head *)0xdead000000000100,
.func = (void (*)(struct callback_head
*))0xdead000000000122,
},
._mapcount = (atomic_t){
.counter = (int)-1,
},
.page_type = (unsigned int)4294967295,
._refcount = (atomic_t){
.counter = (int)1,
},
.memcg_data = (unsigned long)0,
},
._flags_1 = (unsigned long)13510764522373120,
.__head = (unsigned long)18446698392541487105,
._folio_dtor = (unsigned char)1,
._folio_order = (unsigned char)2,
._total_mapcount = (atomic_t){
.counter = (int)-1,
},
._pincount = (atomic_t){
.counter = (int)0,
},
._folio_nr_pages = (unsigned int)4,
}
>>> for index, entry in
xa_for_each(trace[7]['mapping'].i_pages.address_of_()):
print(index, entry, cast('struct folio *',
entry).page.mapping.address_of_())
....
6464 (void *)0xffffd674c130a000 *(struct address_space
**)0xffffd674c130a018 = 0xffffa2b30e93b2b0
6528 (void *)0xffffd674beb22000 *(struct address_space
**)0xffffd674beb22018 = 0xffffa2b30e93b2b0
6592 (void *)0xffffd67406346000 *(struct address_space
**)0xffffd67406346018 = 0x0 <===== our folio
6624 (void *)0x7037e8d8000100d (struct address_space **)0x7037e8d80001025
6625 (void *)0x7037e047000100d (struct address_space **)0x7037e0470001025
....

This looks like the xarray is corrupted, and for some reason we have a
locked folio
in the mapping with a page with no mapping.

Any suggestions on narrowing this down to a hypothesis to try to reproduce this,
or potential fixes are very much appreciated. We are also trying some
different kernels
configurations on different set of hosts to see if the problems go
away for them, such as:
- 6.1.36 without xfs: Support large folios
6795801366da0cd3d99e27c37f020a8f16714886
- 6.1.36 without THP
- 6.1.37 with the following series backported xfs, iomap: fix data
corruption due to stale cached iomaps
https://lore.kernel.org/linux-fsdevel/20221129001632.GX3600936@xxxxxxxxxxxxxxxxxxx/

Best,
Daniel.

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