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

[syzbot]

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: syzbot+8ffca9...@syzkaller.appspotmail.com

Initmem setup node 1 [mem 0x0000000140001000-0x000000023fffffff]
On node 0, zone DMA: 1 pages in unavailable ranges
On node 0, zone DMA: 97 pages in unavailable ranges
On node 0, zone Normal: 3 pages in unavailable ranges
setup_percpu: NR_CPUS:8 nr_cpumask_bits:2 nr_cpu_ids:2 nr_node_ids:2
percpu: Embedded 71 pages/cpu s253896 r8192 d28728 u1048576
pcpu-alloc: s253896 r8192 d28728 u1048576 alloc=1*2097152
pcpu-alloc: [0] 0 1
kvm-guest: PV spinlocks enabled
PV qspinlock hash table entries: 256 (order: 0, 4096 bytes, linear)
Kernel command line: earlyprintk=serial net.ifnames=0 sysctl.kernel.hung_task_all_cpu_backtrace=1 ima_policy=tcb nf-conntrack-ftp.ports=20000 nf-conntrack-tftp.ports=20000 nf-conntrack-sip.ports=20000 nf-conntrack-irc.ports=20000 nf-conntrack-sane.ports=20000 binder.debug_mask=0 rcupdate.rcu_expedited=1 rcupdate.rcu_cpu_stall_cputime=1 no_hash_pointers page_owner=on sysctl.vm.nr_hugepages=4 sysctl.vm.nr_overcommit_hugepages=4 secretmem.enable=1 sysctl.max_rcu_stall_to_panic=1 msr.allow_writes=off coredump_filter=0xffff root=/dev/sda console=ttyS0 vsyscall=native numa=fake=2 kvm-intel.nested=1 spec_store_bypass_disable=prctl nopcid vivid.n_devs=64 vivid.multiplanar=1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2 netrom.nr_ndevs=32 rose.rose_ndevs=32 smp.csd_lock_timeout=100000 watchdog_thresh=55 workqueue.watchdog_thresh=140 sysctl.net.core.netdev_unregister_timeout_secs=140 dummy_hcd.num=32 max_loop=32 nbds_max=32 \
Kernel command line: comedi.comedi_num_legacy_minors=4 panic_on_warn=1 BOOT_IMAGE=/boot/bzImage root=/dev/sda1 console=ttyS0
Unknown kernel command line parameters "nbds_max=32", will be passed to user space.
random: crng init done
printk: log buffer data + meta data: 262144 + 917504 = 1179648 bytes
software IO TLB: area num 2.
Fallback order for Node 0: 0 1
Fallback order for Node 1: 1 0
Built 2 zonelists, mobility grouping on. Total pages: 2097051
Policy zone: Normal
mem auto-init: stack:all(zero), heap alloc:on, heap free:off
stackdepot: allocating hash table via alloc_large_system_hash
stackdepot hash table entries: 1048576 (order: 12, 16777216 bytes, linear)
stackdepot: allocating space for 8192 stack pools via memblock
**********************************************************
** 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 **
**********************************************************
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
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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[Andrew Morton]

(cc Mike Tsirkin)

On Wed, 03 Jun 2026 14:56:25 -0700 syzbot <syzbot+8ffca9...@syzkaller.appspotmail.com> 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: syzbot+8ffca9...@syzkaller.appspotmail.com
>

> ...

>
> **********************************************************
> ** 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/cover.177931...@redhat.com) be
included in -next? It's huge, it's late, review is minor.

<remainder of report is below>

[Michael S. Tsirkin]

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