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

write to 0xffffffff868719b8 of 8 bytes by task 16571 on cpu 1:
 data_alloc+0x31c/0x390 kernel/printk/printk_ringbuffer.c:1130
 prb_reserve+0x964/0xb60 kernel/printk/printk_ringbuffer.c:1724
 vprintk_store+0x56d/0x860 kernel/printk/printk.c:2302
 vprintk_emit+0x15a/0x610 kernel/printk/printk.c:2402
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2441
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2451
 stop_sync_thread+0xff/0x3f0 net/netfilter/ipvs/ip_vs_sync.c:1987
 do_ip_vs_set_ctl+0x2f1/0x8c0 net/netfilter/ipvs/ip_vs_ctl.c:2734
 nf_setsockopt+0x199/0x1b0 net/netfilter/nf_sockopt.c:101
 ip_setsockopt+0x102/0x110 net/ipv4/ip_sockglue.c:1424
 tcp_setsockopt+0x98/0xb0 net/ipv4/tcp.c:4166
 sock_common_setsockopt+0x69/0x80 net/core/sock.c:3972
 smc_setsockopt+0x183/0x750 net/smc/af_smc.c:3097
 do_sock_setsockopt net/socket.c:2322 [inline]
 __sys_setsockopt+0x184/0x200 net/socket.c:2347
 __do_sys_setsockopt net/socket.c:2353 [inline]
 __se_sys_setsockopt net/socket.c:2350 [inline]
 __x64_sys_setsockopt+0x64/0x80 net/socket.c:2350
 x64_sys_call+0x21d5/0x3000 arch/x86/include/generated/asm/syscalls_64.h:55
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd8/0x2a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff868719b8 of 8 bytes by task 16573 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+0x249/0xb60 kernel/printk/printk_ringbuffer.c:1674
 vprintk_store+0x56d/0x860 kernel/printk/printk.c:2302
 vprintk_emit+0x15a/0x610 kernel/printk/printk.c:2402
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2441
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2451
 sync_thread_backup+0xa7/0x1290 net/netfilter/ipvs/ip_vs_sync.c:1709
 kthread+0x489/0x510 kernel/kthread.c:463
 ret_from_fork+0x149/0x290 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

value changed: 0x0000000000150748 -> 0x000000000020d5b0

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 16573 Comm: ipvs-b:503:0 Tainted: G        W           syzkaller #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================
IPVS: sync thread started: state = BACKUP, mcast_ifn = macvtap0, syncid = 5, id = 0