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

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 4 Jun 2026 00:14:35 -0400

On Wed, Jun 03, 2026 at 03:47:37PM -0700, Andrew Morton wrote:
> (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.

Of course not (
I've no idea how that happened.
Should not push to next late at night.

> <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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> > 
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