Re: Softlockup when test shmem swapout-swapin and compaction

[Zi Yan]

On 26 Feb 2025, at 2:22, Baolin Wang wrote:

> Add Zi.
>
> On 2025/2/26 15:03, Liu Shixin wrote:
>> Hi all,
>>
>> I found a softlockup when testing shmem large folio swapout-swapin and compaction:
>>
>>   watchdog: BUG: soft lockup - CPU#30 stuck for 179s! [folio_swap:4714]
>>   Modules linked in: zram xt_MASQUERADE nf_conntrack_netlink nfnetlink iptable_nat xt_addrtype iptable_filter ip_tantel_rapl_msr intel_rapl_common intel_uncore_frequency_common skx_edac_common nfit libnvdimm kvm_intel kvm rapl cixt4 mbcache jbd2 sr_mod cdrom ata_generic ata_piix virtio_net net_failover ghash_clmulni_intel libata sha512_ssse3
>>   CPU: 30 UID: 0 PID: 4714 Comm: folio_swap Kdump: loaded Tainted: G             L     6.14.0-rc4-next-20250225+ #2
>>   Tainted: [L]=SOFTLOCKUP
>>   Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
>>   RIP: 0010:xas_load+0x5d/0xc0
>>   Code: 08 48 d3 ea 83 e2 3f 89 d0 48 83 c0 04 48 8b 44 c6 08 48 89 73 18 48 89 c1 83 e1 03 48 83 f9 02 75 08 48 3d
>>   RSP: 0000:ffffadf142f1ba60 EFLAGS: 00000293
>>   RAX: ffffe524cc4f6700 RBX: ffffadf142f1ba90 RCX: 0000000000000000
>>   RDX: 0000000000000011 RSI: ffff9a3e058acb68 RDI: ffffadf142f1ba90
>>   RBP: fffffffffffffffe R08: ffffadf142f1bb50 R09: 0000000000000392
>>   R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000011
>>   R13: ffffadf142f1bb48 R14: ffff9a3e04e9c588 R15: 0000000000000000
>>   FS:  00007fd957666740(0000) GS:ffff9a41ac0e5000(0000) knlGS:0000000000000000
>>   CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>   CR2: 00007fd922860000 CR3: 000000025c360001 CR4: 0000000000772ef0
>>   DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>>   DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>>   PKRU: 55555554
>>   Call Trace:
>>    <IRQ>
>>    ? watchdog_timer_fn+0x1c9/0x250
>>    ? __pfx_watchdog_timer_fn+0x10/0x10
>>    ? __hrtimer_run_queues+0x10e/0x250
>>    ? hrtimer_interrupt+0xfb/0x240
>>    ? __sysvec_apic_timer_interrupt+0x4e/0xe0
>>    ? sysvec_apic_timer_interrupt+0x68/0x90
>>    </IRQ>
>>    <TASK>
>>    ? asm_sysvec_apic_timer_interrupt+0x16/0x20
>>    ? xas_load+0x5d/0xc0
>>    xas_find+0x153/0x1a0
>>    find_get_entries+0x73/0x280
>>    shmem_undo_range+0x1fc/0x640
>>    shmem_evict_inode+0x109/0x270
>>    evict+0x107/0x240
>>    ? fsnotify_destroy_marks+0x25/0x180
>>    ? _atomic_dec_and_lock+0x35/0x50
>>    __dentry_kill+0x71/0x190
>>    dput+0xd1/0x190
>>    __fput+0x128/0x2a0
>>    task_work_run+0x57/0x90
>>    syscall_exit_to_user_mode+0x1cb/0x1e0
>>    do_syscall_64+0x67/0x170
>>    entry_SYSCALL_64_after_hwframe+0x76/0x7e
>>   RIP: 0033:0x7fd95776eb8b
>>
>> If CONFIG_DEBUG_VM is enabled, we will meet VM_BUG_ON_FOLIO(!folio_test_locked(folio)) in
>> shmem_add_to_page_cache() too.  It seems that the problem is related to memory migration or
>> compaction which is necessary for reproduction,  although without a clear why.
>>
>> To reproduce the problem, we need firstly a zram device as swap backend, and then run the
>> reproduction program. The reproduction program consists of three parts:
>>   1. A process constantly changes the status of shmem large folio by these interfaces:
>>          /sys/kernel/mm/transparent_hugepage/hugepages-<size>/shmem_enabled
>>   2. A process constantly echo 1 > /proc/sys/vm/compact_memory
>>   3. A process constantly alloc/free/swapout/swapin shmem large folios.
>>
>> I'm not sure whether the first process is necessary but the second and third are. In addition,
>> I tried hacking to modify compaction_alloc to return NULL, and the problem disappeared,
>> so I guess the problem is in migration.
>>
>> The problem is different with https://lore.kernel.org/all/1738717785.im3r5g2vxc.none@localhost/
>> since I have confirmed this porblem still existed after merge the fixed patch.
>
> Could you check if your version includes Zi's fix[1]? Not sure if it's related to the shmem large folio split.
>
> [1] https://lore.kernel.org/all/AF487A7A-F685-485D-8D74-756C843D6F0A@xxxxxxxxxx/

Hi Baolin,

With step 2 and 3 above, I hit the error below on mm-everything-2025-03-05-03-54.
It hits VM_BUG_ON_FOLIO(!folio_contains(folio, xas.xa_index), folio).
mm-everything-2025-03-05-03-54 does not have my folio_split() nor xas_try_split()
patches. Can you take a look at it?

What I did:

1. run “while true; do echo 1 | sudo tee /proc/sys/vm/compact_memory >/dev/null; done” to trigger compaction;
2. use zswap with “echo Y | sudo tee /sys/module/zswap/parameters/enabled”;
3. running shmem_aligned_swapin.c you gave me with 128MB SIZE and using
memset(shared_memory, 0xab, SIZE) at the end instead of just setting 0s
(this should not make a difference from your original program).


[   37.591314] page: refcount:2 mapcount:0 mapping:000000000c53d1a6 index:0x6687 pfn:0x169420
[   37.592552] memcg:ffff8881781c1800
[   37.593046] aops:shmem_aops ino:c0f
[   37.593586] flags: 0x2ffff000002013d(locked|referenced|uptodate|dirty|lru|active|swapbacked|node=0|zone=2|lastcpupid=0xffff)
[   37.595138] raw: 02ffff000002013d ffffea00058a6b08 ffffea0005a50408 ffff88817951cd68
[   37.596207] raw: 0000000000006687 0000000000000000 00000002ffffffff ffff8881781c1800
[   37.597305] page dumped because: VM_BUG_ON_FOLIO(!folio_contains(folio, xas.xa_index))
[   37.598464] ------------[ cut here ]------------
[   37.599119] kernel BUG at mm/filemap.c:2134!
[   37.599729] Oops: invalid opcode: 0000 [#1] PREEMPT SMP PTI
[   37.600494] CPU: 4 UID: 1000 PID: 1922 Comm: shmem_aligned_s Not tainted 6.14.0-rc3-mm-everything-2024-01-29-07-19-no-mglru+ #49
[   37.602267] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[   37.603557] RIP: 0010:find_lock_entries+0x352/0x360
[   37.604269] Code: 44 24 10 48 8b 4c 24 18 eb b5 48 c7 c6 08 bb 99 82 4c 89 ff e8 cf e6 03 00 0f 0b 48 c7 c6 70 a3 9c 82 4c 89 ff e8 be e6 03 00 <0f> 0b e8 a7 69 ca 00 0f 1f 80 00 00 00 00 90 90 90 90 90 90 90 9
0
[   37.606838] RSP: 0018:ffffc900029bba68 EFLAGS: 00010246
[   37.607566] RAX: 000000000000004a RBX: fffffffffffffffe RCX: 0000000000000000
[   37.608550] RDX: 0000000000000000 RSI: ffff8882b5d1d900 RDI: ffff8882b5d1d900
[   37.609580] RBP: ffffc900029bba88 R08: 00000000ffffdfff R09: ffffffff82d238c8
[   37.610566] R10: ffffffff82c73920 R11: 6d75642065676170 R12: ffffc900029bbb48
[   37.611551] R13: ffffc900029bbc48 R14: ffff88817951cd68 R15: ffffea0005a50800
[   37.612535] FS:  00007f40107cc740(0000) GS:ffff8882b5d00000(0000) knlGS:0000000000000000
[   37.613683] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   37.614483] CR2: 00007f40107bf000 CR3: 0000000101c00004 CR4: 0000000000370ef0
[   37.615472] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   37.616459] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   37.617481] Call Trace:
[   37.617838]  <TASK>
[   37.618183]  ? __die_body.cold+0x19/0x26
[   37.618746]  ? die+0x2a/0x50
[   37.619150]  ? do_trap+0xc6/0x110
[   37.619610]  ? do_error_trap+0x6a/0x90
[   37.620126]  ? find_lock_entries+0x352/0x360
[   37.620711]  ? exc_invalid_op+0x4c/0x60
[   37.621354]  ? find_lock_entries+0x352/0x360
[   37.622075]  ? asm_exc_invalid_op+0x16/0x20
[   37.622647]  ? find_lock_entries+0x352/0x360
[   37.623268]  ? find_lock_entries+0x352/0x360
[   37.623946]  shmem_undo_range+0xf8/0x6a0
[   37.624547]  shmem_evict_inode+0x117/0x2b0
[   37.625145]  evict+0x10b/0x290
[   37.625607]  ? fsnotify_grab_connector+0x42/0x80
[   37.626257]  ? fsnotify_destroy_marks+0x26/0x1a0
[   37.626903]  ? do_raw_spin_unlock+0x49/0xb0
[   37.627489]  __dentry_kill+0x71/0x1a0
[   37.628009]  dput+0xf8/0x1c0
[   37.628427]  __fput+0x143/0x2b0
[   37.628877]  task_work_run+0x58/0xa0
[   37.629428]  syscall_exit_to_user_mode+0x168/0x170
[   37.630099]  do_syscall_64+0x57/0x110
[   37.630619]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
[   37.631324] RIP: 0033:0x7f40108dc1f7
[   37.631844] Code: 73 01 c3 48 8b 0d 29 9c 0d 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 0b 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d f9 9b 0d 00 f7 d8 64 89 01 4
8
[   37.634424] RSP: 002b:00007ffcad4bd468 EFLAGS: 00000202 ORIG_RAX: 000000000000000b
[   37.635466] RAX: 0000000000000000 RBX: 00007ffcad4bd598 RCX: 00007f40108dc1f7
[   37.636450] RDX: 0000000008000000 RSI: 0000000008000000 RDI: 00007f40087c0000
[   37.637477] RBP: 00007ffcad4bd480 R08: 0000000000000064 R09: 00000000fffffffd
[   37.638460] R10: 0000000000000003 R11: 0000000000000202 R12: 0000000000000000
[   37.639442] R13: 00007ffcad4bd5a8 R14: 00007f4010a10000 R15: 000055694d923dd8
[   37.640422]  </TASK>
[   37.640750] Modules linked in:
[   37.641249] ---[ end trace 0000000000000000 ]---


Best Regards,
Yan, Zi