Re: [syzbot] [nfs?] [io-uring?] WARNING in nfsd_file_cache_init

[Jeff Layton <jlayton@kernel.org>]

On Mon, 2025-10-06 at 22:23 -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    d104e3d17f7b Merge tag 'cxl-for-6.18' of git://git.kernel...
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=116bb942580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=ccc18dddafa95b97
> dashboard link: https://syzkaller.appspot.com/bug?extid=a6f4d69b9b23404bbabf
> compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1573b214580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12b515cd980000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/335d7c35cbbe/disk-d104e3d1.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/72dbd901415b/vmlinux-d104e3d1.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/3ff1353d0870/bzImage-d104e3d1.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+a6f4d69b9b23404bbabf@syzkaller.appspotmail.com
> 
> ------------[ cut here ]------------
> WARNING: CPU: 1 PID: 6128 at kernel/locking/lockdep.c:6606 lockdep_unregister_key+0x2ca/0x310 kernel/locking/lockdep.c:6606
> Modules linked in:
> CPU: 1 UID: 0 PID: 6128 Comm: syz.4.21 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
> RIP: 0010:lockdep_unregister_key+0x2ca/0x310 kernel/locking/lockdep.c:6606
> Code: 50 e4 0f 48 3b 44 24 10 0f 84 26 fe ff ff e8 bd cd 17 09 e8 e8 ce 17 09 41 f7 c7 00 02 00 00 74 bd fb 40 84 ed 75 bc eb cd 90 <0f> 0b 90 e9 19 ff ff ff 90 0f 0b 90 e9 2a ff ff ff 48 c7 c7 d0 ac
> RSP: 0018:ffffc90003e870d0 EFLAGS: 00010002
> RAX: eb1525397f5bdf00 RBX: ffff88803c121148 RCX: 1ffff920007d0dfc
> RDX: 0000000000000000 RSI: ffffffff8acb1500 RDI: ffffffff8b1dd0e0
> RBP: 00000000ffffffea R08: ffffffff8eb5aa37 R09: 1ffffffff1d6b546
> R10: dffffc0000000000 R11: fffffbfff1d6b547 R12: 0000000000000000
> R13: ffff88814d1b8900 R14: 0000000000000000 R15: 0000000000000203
> FS:  00007f773f75e6c0(0000) GS:ffff88812712f000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007ffdaea3af52 CR3: 000000003a5ca000 CR4: 00000000003526f0
> Call Trace:
>  <TASK>
>  __kmem_cache_release+0xe3/0x1e0 mm/slub.c:7696
>  do_kmem_cache_create+0x74e/0x790 mm/slub.c:8575
>  create_cache mm/slab_common.c:242 [inline]
>  __kmem_cache_create_args+0x1ce/0x330 mm/slab_common.c:340
>  nfsd_file_cache_init+0x1d6/0x530 fs/nfsd/filecache.c:816
>  nfsd_startup_generic fs/nfsd/nfssvc.c:282 [inline]
>  nfsd_startup_net fs/nfsd/nfssvc.c:377 [inline]
>  nfsd_svc+0x393/0x900 fs/nfsd/nfssvc.c:786
>  nfsd_nl_threads_set_doit+0x84a/0x960 fs/nfsd/nfsctl.c:1639
>  genl_family_rcv_msg_doit+0x212/0x300 net/netlink/genetlink.c:1115
>  genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
>  genl_rcv_msg+0x60e/0x790 net/netlink/genetlink.c:1210
>  netlink_rcv_skb+0x208/0x470 net/netlink/af_netlink.c:2552
>  genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
>  netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
>  netlink_unicast+0x846/0xa10 net/netlink/af_netlink.c:1346
>  netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1896
>  sock_sendmsg_nosec net/socket.c:727 [inline]
>  __sock_sendmsg+0x219/0x270 net/socket.c:742
>  ____sys_sendmsg+0x508/0x820 net/socket.c:2630
>  ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2684
>  __sys_sendmsg net/socket.c:2716 [inline]
>  __do_sys_sendmsg net/socket.c:2721 [inline]
>  __se_sys_sendmsg net/socket.c:2719 [inline]
>  __x64_sys_sendmsg+0x1a1/0x260 net/socket.c:2719
>  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: 0033:0x7f77400eeec9
> Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007f773f75e038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
> RAX: ffffffffffffffda RBX: 00007f7740345fa0 RCX: 00007f77400eeec9
> RDX: 0000000000008004 RSI: 0000200000000180 RDI: 0000000000000006
> RBP: 00007f7740171f91 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007f7740346038 R14: 00007f7740345fa0 R15: 00007ffce616f8d8
>  </TASK>
> 
> 
> ---
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Pretty sure that this patch broke it:

commit 83382af9ddc3cb0ef43f67d049b461720ad785e6
Author: Alexei Starovoitov <ast@kernel.org>
Date:   Mon Sep 8 18:00:05 2025 -0700

    slab: Make slub local_(try)lock more precise for LOCKDEP

The new lock_key is initialized late in do_kmem_cache_create(), and it
can end up calling __kmem_cache_release() before the lock_key is ever
registered.

-- 
Jeff Layton <jlayton@kernel.org>