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

[Alistair Popple <apopple@nvidia.com>]

On 2026-05-08 at 21:53 +1000, "David Hildenbrand (Arm)" <david@kernel.org> wrote...
> 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?

I haven't managed to reproduce this but could imagine that would be the problem
- not sure page_ext is supported for ZONE_DEVICE PRIVATE pages.

I'm still travelling back from LSFMM so will take a closer look next week.
Thanks!

 - Alistair

> -- 
> Cheers,
> 
> David