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

[Zi Yan <ziy@nvidia.com>]

On 29 Jun 2025, at 18:47, syzbot wrote:

> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    dfba48a70cb6 Merge tag 'i2c-for-6.16-rc4' of git://git.ker..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=14a62982580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=79da270cec5ffd65
> dashboard link: https://syzkaller.appspot.com/bug?extid=359a67b608de1ef72f65
> compiler:       Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-dfba48a7.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/783560258712/vmlinux-dfba48a7.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/685ad235ac7b/bzImage-dfba48a7.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+359a67b608de1ef72f65@syzkaller.appspotmail.com
>
> loop0: detected capacity change from 0 to 32768
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 5325 at mm/page_alloc.c:4430

This warning fires when one tries to allocate a >1 order page with
__GFP_NOFAIL.

> __alloc_pages_slowpath+0xcb3/0xce0 mm/page_alloc.c:4430
> Modules linked in:
> CPU: 0 UID: 0 PID: 5325 Comm: syz.0.0 Not tainted 6.16.0-rc3-syzkaller-00329-gdfba48a70cb6 #0 PREEMPT(full)
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
> RIP: 0010:__alloc_pages_slowpath+0xcb3/0xce0 mm/page_alloc.c:4430
> Code: d8 48 c1 e8 03 0f b6 04 08 84 c0 75 2e f6 43 01 08 48 8b 14 24 0f 84 a2 f3 ff ff 90 0f 0b 90 e9 99 f3 ff ff e8 ae 09 50 09 90 <0f> 0b 90 f7 c5 00 04 00 00 75 bc 90 0f 0b 90 eb b6 89 d9 80 e1 07
> RSP: 0018:ffffc9000d62f970 EFLAGS: 00010246
> RAX: 1378840d66abe400 RBX: 0000000000000002 RCX: dffffc0000000000
> RDX: ffffc9000d62fa80 RSI: 0000000000000002 RDI: 0000000000048cc0
> RBP: 0000000000048cc0 R08: ffff88801b68003f R09: 1ffff110036d0007
> R10: dffffc0000000000 R11: ffffed10036d0008 R12: ffffc9000d62fa80
> R13: 1ffff92001ac5f4c R14: 0000000000048cc0 R15: dffffc0000000000
> FS:  00007fcd1cbf46c0(0000) GS:ffff88808d250000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fcd1bd726e0 CR3: 0000000043166000 CR4: 0000000000352ef0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  __alloc_frozen_pages_noprof+0x319/0x370 mm/page_alloc.c:4972
>  alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2419
>  alloc_slab_page mm/slub.c:2451 [inline]
>  allocate_slab+0xe2/0x3b0 mm/slub.c:2627
>  new_slab mm/slub.c:2673 [inline]

new_slab() allows __GFP_NOFAIL, since GFP_RECLAIM_MASK has it.
In allocate_slab(), the first allocation without __GFP_NOFAIL
failed, the retry used __GFP_NOFAIL but kmem_cache order
was greater than 1, which led to the warning above.

Maybe allocate_slab() should just fail when kmem_cache
order is too big and first trial fails? I am no expert,
so add Vlastimil for help. Barry, who added the nofail
warning is cc’d.


>  ___slab_alloc+0xbfc/0x1480 mm/slub.c:3859
>  __slab_alloc mm/slub.c:3949 [inline]
>  __slab_alloc_node mm/slub.c:4024 [inline]
>  slab_alloc_node mm/slub.c:4185 [inline]
>  __kmalloc_cache_noprof+0x296/0x3d0 mm/slub.c:4354
>  kmalloc_noprof include/linux/slab.h:905 [inline]
>  kzalloc_noprof include/linux/slab.h:1039 [inline]
>  xfs_init_fs_context+0x54/0x500 fs/xfs/xfs_super.c:2279
>  alloc_fs_context+0x651/0x7d0 fs/fs_context.c:318
>  do_new_mount+0x10e/0xa40 fs/namespace.c:3881
>  do_mount fs/namespace.c:4239 [inline]
>  __do_sys_mount fs/namespace.c:4450 [inline]
>  __se_sys_mount+0x317/0x410 fs/namespace.c:4427
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7fcd1bd900ca
> Code: d8 64 89 02 48 c7 c0 ff ff ff ff eb a6 e8 de 1a 00 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007fcd1cbf3e68 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
> RAX: ffffffffffffffda RBX: 00007fcd1cbf3ef0 RCX: 00007fcd1bd900ca
> RDX: 0000200000000040 RSI: 0000200000009640 RDI: 00007fcd1cbf3eb0
> RBP: 0000200000000040 R08: 00007fcd1cbf3ef0 R09: 0000000000208800
> R10: 0000000000208800 R11: 0000000000000246 R12: 0000200000009640
> R13: 00007fcd1cbf3eb0 R14: 000000000000964b R15: 0000200000001340
>  </TASK>
>
>
> ---
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Best Regards,
Yan, Zi