page type is 0, migratetype passed is 2 (nr=256)

["Marc Hartmayer" <mhartmay@linux.ibm.com>]

Hi all,

In a QEMU/KVM guest with 2 vCPUs, when running a test that
enables/disables a vCPU by writing 0 and 1 to the sysfs
`/sys/devices/system/cpu/cpu1/online` in a endless loop and doing some
`dd` operations (block size of 1MB) in the guest in parallel, I
sometimes see the kernel warning:

"page type is 0, migratetype passed is 2 (nr=256)"

The first time this happened was after the warning was added with commit
e0932b6c1f94 (mm: page_alloc: consolidate free page accounting").

Below is a "beautified" (via `decode_stacktrace.sh`) kernel stack trace
(note: it's a self-compiled kernel using the debug config + Linux
v6.15-rc5 + an unrelated patch on top):

```
[   31.079925] page type is 0, passed migratetype is 2 (nr=256)
[   31.079967] WARNING: CPU: 0 PID: 512 at mm/page_alloc.c:668 expand (mm/page_alloc.c:668 (discriminator 2) mm/page_alloc.c:1576 (discriminator 2))
[   31.079974] Modules linked in: essiv authenc dm_crypt encrypted_keys loop pkey_pckmo pkey diag288_wdt watchdog rng_core ghash_s390 prng aes_s390 des_s390 libdes vmw_vsock_virtio_transport vmw_vsock_virtio_transport_common vsock virtio_console vfio_ccw mdev vfio_iommu_type1 sha512_s390 sha256_s390 vfio sha1_s390 sha_common sch_fq_codel drm i2c_core drm_panel_orientation_quirks nfnetlink autofs4 ecdsa_generic ecc
[   31.080051] Hardware name: IBM 2964 NC9 702 (KVM/Linux)
[   31.080055] Krnl PSW : 0404f00180000000 000003339b22f52c expand (mm/page_alloc.c:668 (discriminator 10) mm/page_alloc.c:1576 (discriminator 10))
[   31.080064]            R:0 T:1 IO:0 EX:0 Key:0 M:1 W:0 P:0 AS:3 CC:3 PM:0 RI:0 EA:3
[   31.080071] Krnl GPRS: 0000033380000004 0000000000000005 0000000000000030 00000333ffffffff
[   31.080075]            0000000000000005 0000033380000005 0000000000000100 0000000000000008
[   31.080080]            000003339cf5e290 00000229260c99d8 ffffffff00000008 000002a8827cc000
[   31.080084]            000003ffb7d50b58 0000000000000008 000003339b22f528 000002b39be17240
[ 31.080095] Krnl Code: 000003339b22f51c: c02000936173 larl %r2,000003339c49b802

Code starting with the faulting instruction
===========================================
[   31.080095]            000003339b22f522: c0e5ffe40e37        brasl   %r14,000003339aeb1190
[   31.080095]           #000003339b22f528: af000000            mc      0,0
[   31.080095]           >000003339b22f52c: a7f4ff49            brc     15,000003339b22f3be
[   31.080095]            000003339b22f530: b904002b            lgr     %r2,%r11
[   31.080095]            000003339b22f534: c03000933a81        larl    %r3,000003339c496a36
[   31.080095]            000003339b22f53a: c0e5fffdaad3        brasl   %r14,000003339b1e4ae0
[   31.080095]            000003339b22f540: af000000            mc      0,0
[   31.080123] Call Trace:
[   31.080126] expand (mm/page_alloc.c:668 (discriminator 10) mm/page_alloc.c:1576 (discriminator 10))
[   31.080132] expand (mm/page_alloc.c:668 (discriminator 2) mm/page_alloc.c:1576 (discriminator 2))
[   31.080137] rmqueue_bulk (mm/page_alloc.c:646 mm/page_alloc.c:1592 mm/page_alloc.c:1762 mm/page_alloc.c:2315 mm/page_alloc.c:2368)
[   31.080142] __rmqueue_pcplist (mm/page_alloc.c:3090)
[   31.080147] rmqueue.isra.0 (mm/page_alloc.c:3128 mm/page_alloc.c:3159)
[   31.080153] get_page_from_freelist (mm/page_alloc.c:3687)
[   31.080158] __alloc_frozen_pages_noprof (mm/page_alloc.c:4971 (discriminator 1))
[   31.080164] alloc_pages_mpol (mm/mempolicy.c:2303 (discriminator 1))
[   31.080170] alloc_frozen_pages_noprof (mm/mempolicy.c:2374)
[   31.080176] allocate_slab (mm/slub.c:2454 mm/slub.c:2618)
[   31.080182] ___slab_alloc (mm/slub.c:2672 mm/slub.c:3858)
[   31.080187] __slab_alloc.isra.0 (mm/slub.c:3948)
[   31.080193] kmem_cache_alloc_noprof (mm/slub.c:4023 mm/slub.c:4184 mm/slub.c:4203)
[   31.080199] alloc_buffer_head (fs/buffer.c:3033)
[   31.080204] folio_alloc_buffers (fs/buffer.c:938)
[   31.080212] create_empty_buffers (fs/buffer.c:1697)
[   31.080217] __block_write_begin_int (./include/linux/pagemap.h:1025 fs/buffer.c:2134)
[   31.080222] iomap_write_begin (fs/iomap/buffered-io.c:825)
[   31.080228] iomap_write_iter (fs/iomap/buffered-io.c:952)
[   31.080234] iomap_file_buffered_write (fs/iomap/buffered-io.c:1033 (discriminator 1))
[   31.080240] blkdev_write_iter (block/fops.c:690 block/fops.c:755)
[   31.080246] vfs_write (fs/read_write.c:592 (discriminator 1) fs/read_write.c:684 (discriminator 1) fs/read_write.c:664
 (discriminator 1))
[   31.080251] ksys_write (fs/read_write.c:737)
[   31.080257] __do_syscall (arch/s390/kernel/syscall.c:125 (discriminator 2))
[   31.080262] system_call (arch/s390/kernel/entry.S:263)
[   31.080268] INFO: lockdep is turned off.
[   31.080272] Last Breaking-Event-Address:
[   31.080275] __s390_indirect_jump_r14 (arch/s390/lib/expoline.S:12)
[   31.080284] Kernel panic - not syncing: kernel: panic_on_warn set ...
[   31.080294] Hardware name: IBM 2964 NC9 702 (KVM/Linux)
[   31.080297] Call Trace:
[   31.080300] dump_stack_lvl (lib/dump_stack.c:122)
[   31.080305] panic (kernel/panic.c:372)
[   31.080310] check_panic_on_warn (kernel/panic.c:247)
[   31.080315] __warn (kernel/panic.c:751)
[   31.080321] report_bug (lib/bug.c:176 lib/bug.c:215)
[   31.080327] monitor_event_exception (arch/s390/kernel/traps.c:227 (discriminator 1))
[   31.080333] __do_pgm_check (./arch/s390/include/asm/irqflags.h:48 (discriminator 1) ./arch/s390/include/asm/irqflags.h:86 (discriminator 1) arch/s390/kernel/traps.c:347 (discriminator 1))
[   31.080338] pgm_check_handler (arch/s390/kernel/entry.S:334)
[   31.080344] expand (mm/page_alloc.c:668 (discriminator 10) mm/page_alloc.c:1576 (discriminator 10))
[   31.080349] expand (mm/page_alloc.c:668 (discriminator 2) mm/page_alloc.c:1576 (discriminator 2))
[   31.080353] rmqueue_bulk (mm/page_alloc.c:646 mm/page_alloc.c:1592 mm/page_alloc.c:1762 mm/page_alloc.c:2315 mm/page_a
lloc.c:2368)
[   31.080359] __rmqueue_pcplist (mm/page_alloc.c:3090)
[   31.080364] rmqueue.isra.0 (mm/page_alloc.c:3128 mm/page_alloc.c:3159)
[   31.080369] get_page_from_freelist (mm/page_alloc.c:3687)
[   31.080374] __alloc_frozen_pages_noprof (mm/page_alloc.c:4971 (discriminator 1))
[   31.080380] alloc_pages_mpol (mm/mempolicy.c:2303 (discriminator 1))
[   31.080385] alloc_frozen_pages_noprof (mm/mempolicy.c:2374)
[   31.080390] allocate_slab (mm/slub.c:2454 mm/slub.c:2618)
[   31.080396] ___slab_alloc (mm/slub.c:2672 mm/slub.c:3858)
[   31.080401] __slab_alloc.isra.0 (mm/slub.c:3948)
[   31.080407] kmem_cache_alloc_noprof (mm/slub.c:4023 mm/slub.c:4184 mm/slub.c:4203)
[   31.080412] alloc_buffer_head (fs/buffer.c:3033)
[   31.080417] folio_alloc_buffers (fs/buffer.c:938)
[   31.080422] create_empty_buffers (fs/buffer.c:1697)
[   31.080427] __block_write_begin_int (./include/linux/pagemap.h:1025 fs/buffer.c:2134)
[   31.080433] iomap_write_begin (fs/iomap/buffered-io.c:825)
[   31.080438] iomap_write_iter (fs/iomap/buffered-io.c:952)
[   31.080444] iomap_file_buffered_write (fs/iomap/buffered-io.c:1033 (discriminator 1))
[   31.080449] blkdev_write_iter (block/fops.c:690 block/fops.c:755)
[   31.080455] vfs_write (fs/read_write.c:592 (discriminator 1) fs/read_write.c:684 (discriminator 1) fs/read_write.c:664
 (discriminator 1))
[   31.080460] ksys_write (fs/read_write.c:737)
[   31.080465] __do_syscall (arch/s390/kernel/syscall.c:125 (discriminator 2))
[   31.080470] system_call (arch/s390/kernel/entry.S:263)
[   31.080476] INFO: lockdep is turned off.
```

Any ideas?

--
Thanks in advance,

 Marc