EXT4-fs (loop4): too many log groups per flexible block group
==================================================================
BUG: KCSAN: data-race in data_push_tail / vsnprintf

write to 0xffffffff8936612c of 7 bytes by task 4294 on cpu 1:
 vsnprintf+0x2ce/0x860 lib/vsprintf.c:2899
 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+0x30/0x2b0 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:4930
 dev_printk_emit+0x84/0xb0 drivers/base/core.c:4941
 __netdev_printk+0x34b/0x370 net/core/dev.c:12941
 netdev_info+0xa6/0xd0 net/core/dev.c:12996
 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+0x72/0x1a0 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+0xe2c/0x1650 net/core/dev.c:12421
 unregister_netdevice_many net/core/dev.c:12484 [inline]
 unregister_netdevice_queue+0x1cd/0x200 net/core/dev.c:12294
 unregister_netdevice include/linux/netdevice.h:3444 [inline]
 nsim_destroy+0x15b/0x5a0 drivers/net/netdevsim/netdev.c:1193
 __nsim_dev_port_del+0xd2/0x140 drivers/net/netdevsim/dev.c:1547
 nsim_dev_port_del_all drivers/net/netdevsim/dev.c:1561 [inline]
 nsim_dev_reload_destroy+0x1a3/0x2c0 drivers/net/netdevsim/dev.c:1785
 nsim_dev_reload_down+0x67/0x80 drivers/net/netdevsim/dev.c:1038
 devlink_reload+0xad/0x590 net/devlink/dev.c:462
 devlink_pernet_pre_exit+0xf9/0x260 net/devlink/core.c:558
 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:702
 process_one_work kernel/workqueue.c:3314 [inline]
 process_scheduled_works+0x4f0/0x9c0 kernel/workqueue.c:3397
 worker_thread+0x58a/0x780 kernel/workqueue.c:3478
 kthread+0x22a/0x280 kernel/kthread.c:436
 ret_from_fork+0x146/0x330 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffffffff89366130 of 8 bytes by task 5879 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+0x8d6/0xad0 kernel/printk/printk_ringbuffer.c:1727
 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
 __ext4_msg+0x1aa/0x1c0 fs/ext4/super.c:1001
 ext4_mb_init_backend fs/ext4/mballoc.c:3548 [inline]
 ext4_mb_init+0xcea/0x11a0 fs/ext4/mballoc.c:3848
 __ext4_fill_super fs/ext4/super.c:5654 [inline]
 ext4_fill_super+0x3198/0x37c0 fs/ext4/super.c:5824
 get_tree_bdev_flags+0x291/0x300 fs/super.c:1694
 get_tree_bdev+0x1f/0x30 fs/super.c:1717
 ext4_get_tree+0x1c/0x30 fs/ext4/super.c:5856
 vfs_get_tree+0x57/0x1d0 fs/super.c:1754
 fc_mount fs/namespace.c:1193 [inline]
 do_new_mount_fc fs/namespace.c:3758 [inline]
 do_new_mount+0x288/0x8d0 fs/namespace.c:3834
 path_mount+0x4d0/0xbc0 fs/namespace.c:4154
 do_mount fs/namespace.c:4167 [inline]
 __do_sys_mount fs/namespace.c:4383 [inline]
 __se_sys_mount+0x28c/0x2e0 fs/namespace.c:4360
 __x64_sys_mount+0x67/0x80 fs/namespace.c:4360
 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/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x3fffffffffffe00b -> 0x6d61662032206570

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 5879 Comm: syz.4.457 Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
==================================================================
EXT4-fs (loop4): failed to initialize mballoc (-12)
EXT4-fs (loop4): mount failed