Re: [PATCH 1/1] mm: protect xa split stuff under lruvec->lru_lock during migration

[Marcin Wanat]

On 15.04.2024 03:50, Zhaoyang Huang wrote:
> On Mon, Apr 15, 2024 at 8:09 AM Dave Chinner <david@xxxxxxxxxxxxx> > wrote: >> >> On Sat, Apr 13, 2024 at 10:01:27AM +0800, Zhaoyang 
Huang wrote: >>> loop Dave, since he has ever helped set up an 
reproducer in >>> https://lore.kernel.org/linux- >>> 
mm/20221101071721.GV2703033@xxxxxxxxxxxxxxxxxxx/ @Dave Chinner , >>> I 
would like to ask for your kindly help on if you can verify >>> this 
patch on your environment if convenient. Thanks a lot. >> >> I don't 
have the test environment from 18 months ago available any >> more. 
Also, I haven't seen this problem since that specific test >> 
environment tripped over the issue. Hence I don't have any way of >> 
confirming that the problem is fixed, either, because first I'd >> have 
to reproduce it... > Thanks for the information. I noticed that you 
reported another soft > lockup which is related to xas_load since 
NOV.2023. This patch is > supposed to be helpful for this. With regard 
to the version timing, > this commit is actually a revert of <mm/thp: 
narrow lru locking> > b6769834aac1d467fa1c71277d15688efcbb4d76 which is 
merged before > v5.15. > > For saving your time, a brief description 
below. IMO, b6769834aa > introduce a potential stall between freeze the 
folio's refcnt and > store it back to 2, which have the 
xas_load->folio_try_get_rcu loops > as livelock if it stalls the 
lru_lock's holder. > > b6769834aa split_huge_page_to_list - 
spin_lock(lru_lock) > xas_split(&xas, folio,order) 
folio_refcnt_freeze(folio, 1 + > folio_nr_pages(folio0) + 
spin_lock(lru_lock) xas_store(&xas, > offset++, head+i) 
page_ref_add(head, 2) spin_unlock(lru_lock) > > Sorry in advance if the 
above doesn't make sense, I am just a > developer who is also suffering 
from this bug and trying to fix it
I am experiencing a similar error on dozens of hosts, with stack traces 
that are all similar:

[627163.727746] watchdog: BUG: soft lockup - CPU#77 stuck for 22s! 
[file_get:953301]
[627163.727778] Modules linked in: xt_set ip_set_hash_net ip_set xt_CT 
xt_conntrack nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 nft_compat 
nf_tables nfnetlink sr_mod cdrom rfkill vfat fat intel_rapl_msr 
intel_rapl_common intel_uncore_frequency intel_uncore_frequency_common 
isst_if_common skx_edac nfit libnvdimm x86_pkg_temp_thermal 
intel_powerclamp coretemp ipmi_ssif kvm_intel kvm irqbypass mlx5_ib rapl 
iTCO_wdt intel_cstate intel_pmc_bxt ib_uverbs iTCO_vendor_support 
dell_smbios dcdbas i2c_i801 intel_uncore uas ses mei_me ib_core 
dell_wmi_descriptor wmi_bmof pcspkr enclosure lpc_ich usb_storage 
i2c_smbus acpi_ipmi mei intel_pch_thermal ipmi_si ipmi_devintf 
ipmi_msghandler acpi_power_meter joydev tcp_bbr fuse xfs libcrc32c raid1 
sd_mod sg mlx5_core crct10dif_pclmul crc32_pclmul crc32c_intel 
polyval_clmulni mgag200 polyval_generic drm_kms_helper mlxfw 
drm_shmem_helper ahci nvme mpt3sas tls libahci ghash_clmulni_intel 
nvme_core psample drm igb t10_pi raid_class pci_hyperv_intf dca libata 
scsi_transport_sas i2c_algo_bit wmi
[627163.727841] CPU: 77 PID: 953301 Comm: file_get Kdump: loaded 
Tainted: G             L     6.6.30.el9 #2
[627163.727844] Hardware name: Dell Inc. PowerEdge R740xd/08D89F, BIOS 
2.21.2 02/19/2024
[627163.727847] RIP: 0010:xas_descend+0x1b/0x70
[627163.727857] Code: 57 10 48 89 07 48 c1 e8 20 48 89 57 08 c3 cc 0f b6 
0e 48 8b 47 08 48 d3 e8 48 89 c1 83 e1 3f 89 c8 48 83 c0 04 48 8b 44 c6 
08 <48> 89 77 18 48 89 c2 83 e2 03 48 83 fa 02 74 0a 88 4f 12 c3 48 83
[627163.727859] RSP: 0018:ffffc90034a67978 EFLAGS: 00000206
[627163.727861] RAX: ffff888e4f971242 RBX: ffffc90034a67a98 RCX: 
0000000000000020
[627163.727863] RDX: 0000000000000002 RSI: ffff88a454546d80 RDI: 
ffffc90034a67990
[627163.727865] RBP: fffffffffffffffe R08: fffffffffffffffe R09: 
0000000000008820
[627163.727867] R10: 0000000000008820 R11: 0000000000000000 R12: 
ffffc90034a67a20
[627163.727868] R13: ffffc90034a67a18 R14: ffffea00873e8000 R15: 
ffffc90034a67a18
[627163.727870] FS:  00007fc5e503b740(0000) GS:ffff88bfefd80000(0000) 
knlGS:0000000000000000
[627163.727871] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[627163.727873] CR2: 000000005fb87b6e CR3: 00000022875e8006 CR4: 
00000000007706e0
[627163.727875] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 
0000000000000000
[627163.727876] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 
0000000000000400
[627163.727878] PKRU: 55555554
[627163.727879] Call Trace:
[627163.727882]  <IRQ>
[627163.727886]  ? watchdog_timer_fn+0x22a/0x2a0
[627163.727892]  ? softlockup_fn+0x70/0x70
[627163.727895]  ? __hrtimer_run_queues+0x10f/0x2a0
[627163.727903]  ? hrtimer_interrupt+0x106/0x240
[627163.727906]  ? __sysvec_apic_timer_interrupt+0x68/0x170
[627163.727913]  ? sysvec_apic_timer_interrupt+0x9d/0xd0
[627163.727917]  </IRQ>
[627163.727918]  <TASK>
[627163.727920]  ? asm_sysvec_apic_timer_interrupt+0x16/0x20
[627163.727927]  ? xas_descend+0x1b/0x70
[627163.727930]  xas_load+0x2c/0x40
[627163.727933]  xas_find+0x161/0x1a0
[627163.727937]  find_get_entries+0x77/0x1d0
[627163.727944]  truncate_inode_pages_range+0x244/0x3f0
[627163.727950]  truncate_pagecache+0x44/0x60
[627163.727955]  xfs_setattr_size+0x168/0x490 [xfs]
[627163.728074]  xfs_vn_setattr+0x78/0x140 [xfs]
[627163.728153]  notify_change+0x34f/0x4f0
[627163.728158]  ? _raw_spin_lock+0x13/0x30
[627163.728165]  ? do_truncate+0x80/0xd0
[627163.728169]  do_truncate+0x80/0xd0
[627163.728172]  do_open+0x2ce/0x400
[627163.728177]  path_openat+0x10d/0x280
[627163.728181]  do_filp_open+0xb2/0x150
[627163.728186]  ? check_heap_object+0x34/0x190
[627163.728189]  ? __check_object_size.part.0+0x5a/0x130
[627163.728194]  do_sys_openat2+0x92/0xc0
[627163.728197]  __x64_sys_openat+0x53/0x90
[627163.728200]  do_syscall_64+0x35/0x80
[627163.728206]  entry_SYSCALL_64_after_hwframe+0x4b/0xb5
[627163.728210] RIP: 0033:0x7fc5e493e7fb
[627163.728213] Code: 25 00 00 41 00 3d 00 00 41 00 74 4b 64 8b 04 25 18 
00 00 00 85 c0 75 67 44 89 e2 48 89 ee bf 9c ff ff ff b8 01 01 00 00 0f 
05 <48> 3d 00 f0 ff ff 0f 87 91 00 00 00 48 8b 54 24 28 64 48 2b 14 25
[627163.728215] RSP: 002b:00007ffdd4e300e0 EFLAGS: 00000246 ORIG_RAX: 
0000000000000101
[627163.728218] RAX: ffffffffffffffda RBX: 00007ffdd4e30180 RCX: 
00007fc5e493e7fb
[627163.728220] RDX: 0000000000000241 RSI: 00007ffdd4e30180 RDI: 
00000000ffffff9c
[627163.728221] RBP: 00007ffdd4e30180 R08: 00007fc5e4600040 R09: 
0000000000000001
[627163.728223] R10: 00000000000001b6 R11: 0000000000000246 R12: 
0000000000000241
[627163.728224] R13: 0000000000000000 R14: 00007fc5e4662fa8 R15: 
0000000000000000
[627163.728227]  </TASK>

I have around 50 hosts handling high I/O (each with 20Gbps+ uplinks
and multiple NVMe drives), running RockyLinux 8/9. The stock RHEL
kernel 8/9 is NOT affected, and the long-term kernel 5.15.X is NOT affected.
However, with long-term kernels 6.1.XX and 6.6.XX,
(tested at least 10 different versions), this lockup always appears
after 2-30 days, similar to the report in the original thread.
The more load (for example, copying a lot of local files while
serving 20Gbps traffic), the higher the chance that the bug will appear.

I haven't been able to reproduce this during synthetic tests,
but it always occurs in production on 6.1.X and 6.6.X within 2-30 days.
If anyone can provide a patch, I can test it on multiple machines
over the next few days.

Regards,
Marcin