==================================================================
BUG: KCSAN: data-race in data_alloc / prb_reserve

write to 0xffffffff86c8b1b8 of 8 bytes by interrupt on cpu 1:
 data_alloc+0x308/0x380 kernel/printk/printk_ringbuffer.c:1130
 prb_reserve+0x8e3/0xaf0 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
 buffer_io_error fs/buffer.c:125 [inline]
 end_buffer_async_read fs/buffer.c:308 [inline]
 bh_end_async_read+0x282/0x2b0 fs/buffer.c:415
 bio_endio+0x35b/0x3f0 block/bio.c:1805
 blk_update_request+0x338/0x710 block/blk-mq.c:1016
 blk_mq_end_request+0x26/0x50 block/blk-mq.c:1147
 lo_complete_rq+0x98/0x130 drivers/block/loop.c:314
 blk_complete_reqs block/blk-mq.c:1222 [inline]
 blk_done_softirq+0x77/0xb0 block/blk-mq.c:1227
 handle_softirqs+0xb9/0x280 kernel/softirq.c:622
 run_ksoftirqd+0x1c/0x30 kernel/softirq.c:1076
 smpboot_thread_fn+0x32a/0x510 kernel/smpboot.c:160
 kthread+0x221/0x270 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 0xffffffff86c8b1b8 of 8 bytes by task 29647 on cpu 0:
 desc_read kernel/printk/printk_ringbuffer.c:496 [inline]
 desc_push_tail kernel/printk/printk_ringbuffer.c:792 [inline]
 desc_reserve kernel/printk/printk_ringbuffer.c:938 [inline]
 prb_reserve+0x21a/0xaf0 kernel/printk/printk_ringbuffer.c:1677
 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
 vlan_vid0_add net/8021q/vlan.c:347 [inline]
 vlan_device_event+0xc29/0xcb0 net/8021q/vlan.c:388
 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:2250 [inline]
 call_netdevice_notifiers_extack net/core/dev.c:2288 [inline]
 call_netdevice_notifiers net/core/dev.c:2302 [inline]
 __dev_notify_flags+0x1f0/0x390 net/core/dev.c:-1
 netif_change_flags+0xa5/0xc0 net/core/dev.c:9822
 do_setlink+0x8fc/0x2860 net/core/rtnetlink.c:3215
 rtnl_changelink net/core/rtnetlink.c:3849 [inline]
 __rtnl_newlink net/core/rtnetlink.c:4022 [inline]
 rtnl_newlink+0x1086/0x1400 net/core/rtnetlink.c:4159
 rtnetlink_rcv_msg+0x64b/0x720 net/core/rtnetlink.c:7076
 netlink_rcv_skb+0x11e/0x220 net/netlink/af_netlink.c:2556
 rtnetlink_rcv+0x1c/0x30 net/core/rtnetlink.c:7103
 netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
 netlink_unicast+0x5a7/0x680 net/netlink/af_netlink.c:1345
 netlink_sendmsg+0x5be/0x6f0 net/netlink/af_netlink.c:1900
 sock_sendmsg_nosec net/socket.c:775 [inline]
 __sock_sendmsg net/socket.c:790 [inline]
 __sys_sendto+0x411/0x470 net/socket.c:2252
 __do_sys_sendto net/socket.c:2259 [inline]
 __se_sys_sendto net/socket.c:2255 [inline]
 __x64_sys_sendto+0x76/0x90 net/socket.c:2255
 x64_sys_call+0x2d35/0x3020 arch/x86/include/generated/asm/syscalls_64.h:45
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000000000548c8 -> 0x0000000000108a08

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 29647 Comm: syz-executor Tainted: G        W           syzkaller #0 PREEMPT(lazy) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
==================================================================
8021q: adding VLAN 0 to HW filter on device batadv0
veth0_vlan: entered promiscuous mode
veth1_vlan: entered promiscuous mode
veth0_macvtap: entered promiscuous mode
veth1_macvtap: entered promiscuous mode
batman_adv: batadv0: Interface activated: batadv_slave_0
batman_adv: batadv0: Interface activated: batadv_slave_1