Re: "alloc_tag was not set" when running mm/ksft_hmm.sh

[David Hildenbrand (Arm)]

On 5/6/26 17:42, Zenghui Yu wrote:
> Hi all,
> 
> Running mm/ksft_hmm.sh triggers the following splat:
> 
>  ------------[ cut here ]------------
>  alloc_tag was not set
>  WARNING: ./include/linux/alloc_tag.h:164 at ___free_pages+0x2a0/0x2d0,
> CPU#5: hmm-tests/2020
>  Modules linked in: test_hmm rfkill drm backlight fuse
>  CPU: 5 UID: 0 PID: 2020 Comm: hmm-tests Kdump: loaded Not tainted
> 7.1.0-rc2-00099-gadc1e5c6203c-dirty #285 PREEMPT
>  Hardware name: QEMU QEMU Virtual Machine, BIOS
> edk2-stable202408-prebuilt.qemu.org 08/13/2024
>  pstate: 61400005 (nZCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
>  pc : ___free_pages+0x2a0/0x2d0
>  lr : ___free_pages+0x2a0/0x2d0
>  sp : ffff80008345b530
>  x29: ffff80008345b530 x28: ffff80008345b700 x27: ffffffffbfff8040
>  x26: ffff0000c41cb360 x25: ffff0000c0c64008 x24: ffff800081aae400
>  x23: 05ffff0000000200 x22: 0000000000000000 x21: 0000000000000000
>  x20: fffffdffc5f20040 x19: 0000000000000000 x18: fffffffffffe7c78
>  x17: 0000000000000000 x16: 0000000000000000 x15: fffffffffffe7c98
>  x14: 00000000000001d1 x13: ffff8000818f3d58 x12: 0000000000000573
>  x11: fffffffffffe7c98 x10: ffff80008194bd58 x9 : 3ffffffffffff000
>  x8 : ffff8000818f3d58 x7 : ffff80008194bd58 x6 : 0000000000000000
>  x5 : ffff0001fedb1088 x4 : 0000000000000001 x3 : 0000000000000000
>  x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff0000c7f58000
>  Call trace:
>   ___free_pages+0x2a0/0x2d0 (P)
>   __free_pages+0x14/0x20
>   dmirror_devmem_free+0x13c/0x158 [test_hmm]
>   free_zone_device_folio+0x144/0x1e4
>   __folio_put+0x124/0x130
>   free_folio_and_swap_cache+0xa8/0xcc
>   __folio_split+0x664/0x7fc
>   split_folio_to_list+0x50/0x5c
>   migrate_vma_split_folio+0x13c/0x25c
>   migrate_vma_collect_pmd+0xed4/0xf68
>   walk_pgd_range+0x598/0x9a0
>   __walk_page_range+0x90/0x1a0
>   walk_page_range_mm_unsafe+0x194/0x20c
>   walk_page_range+0x20/0x2c
>   migrate_vma_setup+0x18c/0x224
>   dmirror_devmem_fault+0x188/0x2b8 [test_hmm]
>   do_swap_page+0x1458/0x185c
>   __handle_mm_fault+0x85c/0x1ba0
>   handle_mm_fault+0xb0/0x290
>   do_page_fault+0x1f8/0x6f8
>   do_translation_fault+0x60/0x6c
>   do_mem_abort+0x44/0x94
>   el0_da+0x30/0xdc
>   el0t_64_sync_handler+0xd0/0xe4
>   el0t_64_sync+0x198/0x19c
>  ---[ end trace 0000000000000000 ]---
>  lib/test_hmm.c:705 module test_hmm func:dmirror_devmem_alloc_page has
> 16744448 allocated at module unload
> 
> 
> It was tested on kernel built with arm64's virt.config and
> 
> +CONFIG_ZONE_DEVICE=y
> +CONFIG_DEVICE_PRIVATE=y
> +CONFIG_TEST_HMM=m
> +CONFIG_MEM_ALLOC_PROFILING=y
> +CONFIG_MEM_ALLOC_PROFILING_DEBUG=y

I assume there is a weird interaction between alloc tags and simulated
ZONE_DEVICE memory in test_hmm.c

@Alistair, any idea?

-- 
Cheers,

David