Re: [syzbot] [mm?] WARNING in mmap_region

[Lorenzo Stoakes (ARM)]

On Sat, Aug 08, 2026 at 01:10:31PM -0700, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    1701fda2f58e Add linux-next specific files for 20260805
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=120a0fb9580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=1abaff330e312dba
> dashboard link: https://syzkaller.appspot.com/bug?extid=d3c6764857d7cac5048a
> compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1255d7b9580000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/260da702bc71/disk-1701fda2.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/006e50e3e545/vmlinux-1701fda2.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/232c4643654a/bzImage-1701fda2.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+d3c6764857d7cac5048a@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> ------------[ cut here ]------------
> vma_is_anonymous(vma)
> WARNING: mm/internal.h:241 at mmap_file mm/internal.h:241 [inline], CPU#0: syz.0.17/5892

This is:

	/* Hooks cannot mark themselves anonymous. */
	if (WARN_ON_ONCE(vma_is_anonymous(vma)))
		err = -EINVAL;

And this is a known bug that was addressed in v3 of my series (which is
currently at v4) - commit 1701fda2f58e (next-20260805) has the v2 (master has
v4).

Pertinent change:

- Fixed an issue with drivers that intentionally mark vma->vm_ops as NULL
  (using the legacy ->mmap callback). If they do this set dummy ops, which
  is what they meant. The mmap_prepare case is fine as nobody does this
  there and this will be fixed when all drivers are finally converted to
  mmap_prepare. As reported by Sashiko.

>From https://lore.kernel.org/all/20260729-b4-scalable-cow-virt-pgoff-v3-0-e8ecfefea812@xxxxxxxxxx/

And the stack below suggests this is the mmap path as expected (no mmap_prepare
callback does this :)

So TL;DR - this is already fixed - nothing to see here folks :)

> WARNING: mm/internal.h:241 at __mmap_new_file_vma mm/vma.c:2586 [inline], CPU#0: syz.0.17/5892
> WARNING: mm/internal.h:241 at __mmap_new_vma mm/vma.c:2685 [inline], CPU#0: syz.0.17/5892
> WARNING: mm/internal.h:241 at __mmap_region mm/vma.c:2905 [inline], CPU#0: syz.0.17/5892
> WARNING: mm/internal.h:241 at mmap_region+0x1f8d/0x2460 mm/vma.c:2990, CPU#0: syz.0.17/5892
> Modules linked in:
> CPU: 0 UID: 0 PID: 5892 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
> RIP: 0010:mmap_file mm/internal.h:241 [inline]
> RIP: 0010:__mmap_new_file_vma mm/vma.c:2586 [inline]
> RIP: 0010:__mmap_new_vma mm/vma.c:2685 [inline]
> RIP: 0010:__mmap_region mm/vma.c:2905 [inline]
> RIP: 0010:mmap_region+0x1f8d/0x2460 mm/vma.c:2990
> Code: d6 a0 ff e9 69 f1 ff ff e8 10 d6 a0 ff 90 0f 0b 90 e9 5f e2 ff ff e8 02 d6 a0 ff 90 0f 0b 90 e9 02 fe ff ff e8 f4 d5 a0 ff 90 <0f> 0b 90 c7 44 24 08 ea ff ff ff 48 b8 00 00 00 00 00 fc ff df 41
> RSP: 0018:ffffc900037bf560 EFLAGS: 00010293
> RAX: ffffffff8226adfc RBX: fffff520006f7ec0 RCX: ffff88801d711f40
> RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000000000000001
> RBP: ffffc900037bfb70 R08: ffff8880122eb803 R09: 1ffff1100245d700
> R10: dffffc0000000000 R11: ffffed100245d701 R12: dffffc0000000000
> R13: 1ffff920006f7efd R14: 1ffff11006c41e09 R15: ffff88803620f048
> FS:  0000555564503500(0000) GS:ffff888124f18000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fa7f9a70000 CR3: 0000000071f6c000 CR4: 00000000003526f0
> Call Trace:
>  <TASK>
>  do_mmap+0xe0a/0x1300 mm/mmap.c:573
>  vm_mmap_pgoff+0x272/0x4e0 mm/util.c:581
>  ksys_mmap_pgoff+0x4dc/0x760 mm/mmap.c:619
>  do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
>  do_syscall_64+0x166/0x510 arch/x86/entry/syscall_64.c:84
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7fa7f9b9e0d9
> Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007fffcfdacab8 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
> RAX: ffffffffffffffda RBX: 00007fa7f9e25fa0 RCX: 00007fa7f9b9e0d9
> RDX: 0000000002000000 RSI: 0000000000003000 RDI: 0000200000ffa000
> RBP: 00007fa7f9c35024 R08: 0000000000000003 R09: 0000000100000000
> R10: 0000000000000013 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007fa7f9e25fac R14: 00007fa7f9e25fa0 R15: 00007fa7f9e25fa0
>  </TASK>
>
>
> ---
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--
Cheers, Lorenzo