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

[Zi Yan <ziy@nvidia.com>]

On 12 May 2025, at 12:16, Lorenzo Stoakes wrote:

> +cc Zi
>
> Hi Marc,
>
> I noticed this same bug as reported in [0], but only for a _very_ recent
> patch series by Zi, which is only present in mm-new, which is the most
> unstable mm branch right now :)
>
> So I wonder if related or a coincidence caused by something else?

Unless Marc's branch has my "make MIGRATE_ISOLATE a standalone bit" patchset,
it should be caused by something else.

A bisect would be very helpful.

>
> This is triggered by the mm self-test (in tools/testing/selftests/mm, you
> can just make -jXX there) transhuge-stress, invoked as:
>
> $ sudo ./transhuge-stress -d 20
>
> The stack traces do look very different though so perhaps unrelated?

The warning is triggered, in the both cases, a pageblock with MIGRATE_UNMOVABLE(0)
is moved to MIGRATE_RECLAIMABLE(2). The pageblock is supposed to have
MIGRATE_RECLAIMABLE(2) before the movement.

>
> Cheers, Lorenzo
>
> [0]: https://lore.kernel.org/linux-mm/ef5f6776-b405-48e8-9fa9-c56af392bc4f@lucifer.local/#t
>
> On Mon, May 12, 2025 at 04:18:06PM +0200, Marc Hartmayer wrote:
>> 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
>>
>>


--
Best Regards,
Yan, Zi