Subject: Re: [syzbot] [mm?] linux-next test error: kernel BUG in post_alloc_hook

From: Andrew Morton <[email-masked]>
Date: Wed, 3 Jun 2026 15:47:37 -0700

(cc Mike Tsirkin)

On Wed, 03 Jun 2026 14:56:25 -0700 syzbot <[email-masked]> wrote:

> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    a225caacc365 Add linux-next specific files for 20260603
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=13b0de66580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=717edf2a5f9fc390
> dashboard link: https://syzkaller.appspot.com/bug?extid=8ffca916f3fa5455f9b4
> compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/f799d07ea17d/disk-a225caac.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/72d0f0ff94e6/vmlinux-a225caac.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/99d4279e6fec/bzImage-a225caac.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: [email-masked]
> 
> ...
>
> **********************************************************
> **   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **
> **                                                      **
> ** This system shows unhashed kernel memory addresses   **
> ** via the console, logs, and other interfaces. This    **
> ** might reduce the security of your system.            **
> **                                                      **
> ** If you see this message and you are not debugging    **
> ** the kernel, report this immediately to your system   **
> ** administrator!                                       **
> **                                                      **
> ** Use hash_pointers=always to force this mode off      **
> **                                                      **
> **   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **
> **********************************************************

Geeze, who added that.

> page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x13fe38
> head: order:2 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
> flags: 0x100000000000040(head|node=0|zone=2)
> raw: 0100000000000040 dead000000000100 dead000000000122 0000000000000000
> raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
> head: 0100000000000040 dead000000000100 dead000000000122 0000000000000000
> head: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
> head: 0100000000000002 ffffffffffffff01 00000000ffffffff 00000000ffffffff
> head: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000004
> page dumped because: VM_BUG_ON_PAGE(1 && PageCompound(page))
> ------------[ cut here ]------------
> kernel BUG at ./include/linux/page-flags.h:682!
> Oops: invalid opcode: 0000 [#1] SMP KASAN PTI
> CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted syzkaller #0 PREEMPT_{RT,(undef)} 
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
> RIP: 0010:__ClearPagePrezeroed include/linux/page-flags.h:682 [inline]
> RIP: 0010:post_alloc_hook+0x287/0x310 mm/page_alloc.c:1863

That's the __ClearPagePrezeroed(page) added by 504f40f6bda6 ("mm:
page_reporting: skip redundant zeroing of host-zeroed reported pages").

Was it intended that this series
(https://lore.kernel.org/[email-masked]) be
included in -next?  It's huge, it's late, review is minor.

<remainder of report is below>

> Code: ff ff 89 da be 01 00 00 00 48 c7 c7 40 50 4f 8e e8 ce 4b d4 02 e9 c5 fe ff ff 4c 89 ef 48 c7 c6 40 ef 7a 8b e8 2a c6 05 ff 90 <0f> 0b 31 ed f7 44 24 04 00 01 00 00 0f 84 8e fd ff ff e9 86 fd ff
> RSP: 0000:ffffffff8e0078e0 EFLAGS: 00010046
> RAX: 0000000000000000 RBX: 0000000000000002 RCX: ffffffff8e0fef40
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
> RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000000
> R10: dffffc0000000000 R11: ffffed10170c4903 R12: dffffc0000000000
> R13: ffffea0004ff8e00 R14: 1ffffd40009ff1c0 R15: 0000000000000000
> FS:  0000000000000000(0000) GS:ffff888125a79000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: ffff88823ffff000 CR3: 000000000e1b8000 CR4: 00000000000100b0
> Call Trace:
>  <TASK>
>  prep_new_page mm/page_alloc.c:1925 [inline]
>  get_page_from_freelist+0x3081/0x3320 mm/page_alloc.c:4015
>  __alloc_frozen_pages_noprof+0x194/0x380 mm/page_alloc.c:5376
>  __alloc_pages_mpol+0xe0/0x390 mm/mempolicy.c:2495
>  alloc_slab_page mm/slub.c:3287 [inline]
>  allocate_slab+0x83/0x5e0 mm/slub.c:3404
>  new_slab mm/slub.c:3447 [inline]
>  ___slab_alloc+0x160/0x930 mm/slub.c:4485
>  __slab_alloc_node mm/slub.c:4549 [inline]
>  slab_alloc_node mm/slub.c:4925 [inline]
>  __do_kmalloc_node mm/slub.c:5331 [inline]
>  __kmalloc_noprof+0x140/0x7b0 mm/slub.c:5345
>  _kmalloc_noprof include/linux/slab.h:973 [inline]
>  _kzalloc_noprof include/linux/slab.h:1286 [inline]
>  __alloc_empty_sheaf mm/slub.c:2774 [inline]
>  alloc_empty_sheaf mm/slub.c:2794 [inline]
>  init_percpu_sheaves mm/slub.c:7555 [inline]
>  do_kmem_cache_create+0x8ae/0x9a0 mm/slub.c:8595
>  create_boot_cache+0xbf/0x120 mm/slab_common.c:717
>  create_kmalloc_cache+0x41/0xb0 mm/slab_common.c:735
>  new_kmalloc_cache+0xd4/0x180 mm/slab_common.c:982
>  create_kmalloc_caches+0x14/0x50 mm/slab_common.c:1005
>  kmem_cache_init+0x14a/0x1e0 mm/slub.c:8496
>  mm_core_init+0x7e/0xb0 mm/mm_init.c:2728
>  start_kernel+0x162/0x3e0 init/main.c:1034
>  x86_64_start_reservations+0x24/0x30 arch/x86/kernel/head64.c:310
>  x86_64_start_kernel+0x143/0x1c0 arch/x86/kernel/head64.c:291
>  common_startup_64+0x13e/0x157
>  </TASK>
> Modules linked in:
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:__ClearPagePrezeroed include/linux/page-flags.h:682 [inline]
> RIP: 0010:post_alloc_hook+0x287/0x310 mm/page_alloc.c:1863
> Code: ff ff 89 da be 01 00 00 00 48 c7 c7 40 50 4f 8e e8 ce 4b d4 02 e9 c5 fe ff ff 4c 89 ef 48 c7 c6 40 ef 7a 8b e8 2a c6 05 ff 90 <0f> 0b 31 ed f7 44 24 04 00 01 00 00 0f 84 8e fd ff ff e9 86 fd ff
> RSP: 0000:ffffffff8e0078e0 EFLAGS: 00010046
> RAX: 0000000000000000 RBX: 0000000000000002 RCX: ffffffff8e0fef40
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
> RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000000
> R10: dffffc0000000000 R11: ffffed10170c4903 R12: dffffc0000000000
> R13: ffffea0004ff8e00 R14: 1ffffd40009ff1c0 R15: 0000000000000000
> FS:  0000000000000000(0000) GS:ffff888125a79000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: ffff88823ffff000 CR3: 000000000e1b8000 CR4: 00000000000100b0
> 
> 
> ---
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