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BUG: KCSAN: data-race in desc_read_finalized_seq / prb_reserve

write to 0xffffffff86920d70 of 8 bytes by task 31271 on cpu 1:
 prb_reserve+0x750/0xb80
 vprintk_store+0x552/0x860 kernel/printk/printk.c:2326
 vprintk_emit+0x174/0x6a0 kernel/printk/printk.c:2408
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2447
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x7f/0xb0 kernel/printk/printk.c:2457
 ip_vs_scheduler_err+0x186/0x190
 ip_vs_wlc_schedule+0xa0/0x1d0 net/netfilter/ipvs/ip_vs_wlc.c:58
 ip_vs_sched_persist net/netfilter/ipvs/ip_vs_core.c:353 [inline]
 ip_vs_schedule+0x86f/0xe00 net/netfilter/ipvs/ip_vs_core.c:508
 udp_conn_schedule+0x254/0x3c0 net/netfilter/ipvs/ip_vs_proto_udp.c:78
 ip_vs_try_to_schedule net/netfilter/ipvs/ip_vs_core.c:1482 [inline]
 ip_vs_in_hook+0x742/0x1230 net/netfilter/ipvs/ip_vs_core.c:2054
 nf_hook_entry_hookfn include/linux/netfilter.h:154 [inline]
 nf_hook_slow+0x89/0x1b0 net/netfilter/core.c:626
 nf_hook include/linux/netfilter.h:269 [inline]
 __ip_local_out+0x2d4/0x300 net/ipv4/ip_output.c:119
 ip_local_out net/ipv4/ip_output.c:128 [inline]
 ip_send_skb+0x30/0x140 net/ipv4/ip_output.c:1502
 udp_send_skb+0x6c2/0xa10 net/ipv4/udp.c:1196
 udp_sendmsg+0x12c1/0x1360 net/ipv4/udp.c:1484
 inet_sendmsg+0xaf/0xd0 net/ipv4/af_inet.c:851
 sock_sendmsg_nosec net/socket.c:718 [inline]
 __sock_sendmsg+0x102/0x180 net/socket.c:733
 ____sys_sendmsg+0x350/0x4e0 net/socket.c:2573
 ___sys_sendmsg net/socket.c:2627 [inline]
 __sys_sendmmsg+0x22a/0x4b0 net/socket.c:2716
 __do_sys_sendmmsg net/socket.c:2743 [inline]
 __se_sys_sendmmsg net/socket.c:2740 [inline]
 __x64_sys_sendmmsg+0x57/0x70 net/socket.c:2740
 x64_sys_call+0x2b53/0x2e10 arch/x86/include/generated/asm/syscalls_64.h:308
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff86920d70 of 8 bytes by task 31238 on cpu 0:
 desc_read kernel/printk/printk_ringbuffer.c:486 [inline]
 desc_read_finalized_seq+0x163/0x280 kernel/printk/printk_ringbuffer.c:1874
 prb_read kernel/printk/printk_ringbuffer.c:1922 [inline]
 _prb_read_valid+0x142/0x6c0 kernel/printk/printk_ringbuffer.c:2113
 prb_read_valid+0x42/0x70 kernel/printk/printk_ringbuffer.c:2182
 printk_get_next_message+0xdc/0x530 kernel/printk/printk.c:2987
 console_emit_next_record kernel/printk/printk.c:3074 [inline]
 console_flush_all+0x2a9/0x7a0 kernel/printk/printk.c:3208
 __console_flush_and_unlock kernel/printk/printk.c:3267 [inline]
 console_unlock+0xf4/0x350 kernel/printk/printk.c:3307
 con_flush_chars+0xb0/0x1b0 drivers/tty/vt/vt.c:3503
 n_tty_write+0x97d/0xb80 drivers/tty/n_tty.c:2405
 iterate_tty_write drivers/tty/tty_io.c:1015 [inline]
 file_tty_write+0x382/0x6a0 drivers/tty/tty_io.c:1090
 tty_write+0x28/0x30 drivers/tty/tty_io.c:1111
 new_sync_write fs/read_write.c:591 [inline]
 vfs_write+0x79b/0x950 fs/read_write.c:684
 ksys_write+0xeb/0x1b0 fs/read_write.c:736
 __do_sys_write fs/read_write.c:747 [inline]
 __se_sys_write fs/read_write.c:744 [inline]
 __x64_sys_write+0x42/0x50 fs/read_write.c:744
 x64_sys_call+0x2a45/0x2e10 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000003952 -> 0x0000000000005952

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 31238 Comm: syz.9.10370 Tainted: G        W          6.14.0-syzkaller-01103-g2df0c02dab82 #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
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