[moderation] [kernel?] KCSAN: data-race in data_push_tail / number (6)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: ecc64d2dc9ff Merge tag 'sysctl-7.00-fixes-rc3' of git://gi..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17a01552580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6b32b22d8934c136
dashboard link: https://syzkaller.appspot.com/bug?extid=1d075e8baf3ef5de6b31
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [da...@kernel.org drive...@lists.linux.dev gre...@linuxfoundation.org linux-...@vger.kernel.org raf...@kernel.org]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/955ded1e4b51/disk-ecc64d2d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/def9de522048/vmlinux-ecc64d2d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/1354202b5017/bzImage-ecc64d2d.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+1d075e...@syzkaller.appspotmail.com

loop2: detected capacity change from 0 to 128
vfat: Unknown parameter '����������000000000000000000006ɲ �� 1 � �s�{���T�6�+� �`�N�+�%{a �ZI֝����` �� 1
�wM OA��y��%(�4�ab�V۾8 �_Kׂ(W6 ��>� $ �B�Z'
==================================================================
BUG: KCSAN: data-race in data_push_tail / number

write to 0xffffffff893c2708 of 1 bytes by task 12636 on cpu 1:
number+0x865/0xb90 lib/vsprintf.c:573
vsnprintf+0x64e/0x860 lib/vsprintf.c:2912
va_format lib/vsprintf.c:1723 [inline]
pointer+0x821/0xcb0 lib/vsprintf.c:2569
vsnprintf+0x491/0x860 lib/vsprintf.c:2952
vscnprintf+0x41/0x90 lib/vsprintf.c:3013
printk_sprint+0x30/0x2e0 kernel/printk/printk.c:2222
vprintk_store+0x57b/0x910 kernel/printk/printk.c:2364
vprintk_emit+0x1a4/0x600 kernel/printk/printk.c:2455
dev_vprintk_emit+0x242/0x2a0 drivers/base/core.c:4913
dev_printk_emit+0x84/0xb0 drivers/base/core.c:4924
__netdev_printk+0x34b/0x370 net/core/dev.c:12932
netdev_info+0xa6/0xd0 net/core/dev.c:12987
nsim_udp_tunnel_unset_port+0x190/0x1b0 drivers/net/netdevsim/udp_tunnels.c:59
udp_tunnel_nic_device_sync_one net/ipv4/udp_tunnel_nic.c:-1 [inline]
udp_tunnel_nic_device_sync_by_port net/ipv4/udp_tunnel_nic.c:249 [inline]
__udp_tunnel_nic_device_sync+0x575/0x9b0 net/ipv4/udp_tunnel_nic.c:292
udp_tunnel_nic_flush+0x21b/0x300 net/ipv4/udp_tunnel_nic.c:694
udp_tunnel_nic_unregister net/ipv4/udp_tunnel_nic.c:901 [inline]
udp_tunnel_nic_netdevice_event+0x8c0/0xd70 net/ipv4/udp_tunnel_nic.c:942
notifier_call_chain kernel/notifier.c:85 [inline]
raw_notifier_call_chain+0x83/0x1c0 kernel/notifier.c:453
call_netdevice_notifiers_info net/core/dev.c:2249 [inline]
call_netdevice_notifiers_extack net/core/dev.c:2287 [inline]
call_netdevice_notifiers net/core/dev.c:2301 [inline]
unregister_netdevice_many_notify+0xedb/0x1710 net/core/dev.c:12412
unregister_netdevice_many net/core/dev.c:12475 [inline]
unregister_netdevice_queue+0x1cd/0x200 net/core/dev.c:12289
unregister_netdevice include/linux/netdevice.h:3408 [inline]
nsim_destroy+0x108/0x480 drivers/net/netdevsim/netdev.c:1182
__nsim_dev_port_del+0xcf/0x110 drivers/net/netdevsim/dev.c:1528
nsim_dev_port_del_all drivers/net/netdevsim/dev.c:1540 [inline]
nsim_dev_reload_destroy+0x1a3/0x2c0 drivers/net/netdevsim/dev.c:1764
nsim_dev_reload_down+0x67/0x80 drivers/net/netdevsim/dev.c:1038
devlink_reload+0xad/0x590 net/devlink/dev.c:461
devlink_pernet_pre_exit+0xdb/0x230 net/devlink/core.c:507
ops_pre_exit_list net/core/net_namespace.c:161 [inline]
ops_undo_list+0xb5/0x420 net/core/net_namespace.c:234
cleanup_net+0x37c/0x5b0 net/core/net_namespace.c:704
process_one_work kernel/workqueue.c:3275 [inline]
process_scheduled_works+0x4de/0x9e0 kernel/workqueue.c:3358
worker_thread+0x581/0x770 kernel/workqueue.c:3439
kthread+0x22a/0x280 kernel/kthread.c:467
ret_from_fork+0x150/0x360 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffffffff893c2708 of 8 bytes by task 26268 on cpu 0:
data_make_reusable kernel/printk/printk_ringbuffer.c:608 [inline]
data_push_tail+0x100/0x470 kernel/printk/printk_ringbuffer.c:693
data_alloc+0x11b/0x390 kernel/printk/printk_ringbuffer.c:1089
prb_reserve+0x8d7/0xae0 kernel/printk/printk_ringbuffer.c:1724
vprintk_store+0x54a/0x910 kernel/printk/printk.c:2354
vprintk_emit+0x1a4/0x600 kernel/printk/printk.c:2455
vprintk_default+0x26/0x30 kernel/printk/printk.c:2494
vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
_printk+0x79/0xa0 kernel/printk/printk.c:2504
logfc+0x2d5/0x2e0 fs/fs_context.c:-1
vfs_parse_fs_param+0x1e0/0x2a0 fs/fs_context.c:144
vfs_parse_fs_qstr fs/fs_context.c:173 [inline]
vfs_parse_fs_string include/linux/fs_context.h:142 [inline]
vfs_parse_monolithic_sep+0x1e6/0x270 fs/fs_context.c:213
generic_parse_monolithic+0x24/0x30 fs/fs_context.c:241
parse_monolithic_mount_data+0x46/0x60 fs/fs_context.c:520
do_new_mount+0x24e/0x8d0 fs/namespace.c:3835
path_mount+0x4d0/0xbc0 fs/namespace.c:4159
do_mount fs/namespace.c:4172 [inline]
__do_sys_mount fs/namespace.c:4361 [inline]
__se_sys_mount+0x28c/0x2e0 fs/namespace.c:4338
__x64_sys_mount+0x67/0x80 fs/namespace.c:4338
x64_sys_call+0x2d61/0x3020 arch/x86/include/generated/asm/syscalls_64.h:166
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000000fffff9d2 -> 0x7974205d31202c31

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 26268 Comm: syz.2.2946 Tainted: G W syzkaller #0 PREEMPT(full)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
==================================================================
lo speed is unknown, defaulting to 1000


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