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

write to 0xffffffff86a86ba0 of 8 bytes by interrupt on cpu 1:
 data_alloc+0x31c/0x390 kernel/printk/printk_ringbuffer.c:1130
 prb_reserve+0x8d7/0xae0 kernel/printk/printk_ringbuffer.c:1724
 vprintk_store+0x54a/0x910 kernel/printk/printk.c:2302
 vprintk_emit+0x1a4/0x600 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
 ip_vs_scheduler_err+0x190/0x1a0 net/netfilter/ipvs/ip_vs_sched.c:-1
 ip_vs_dh_schedule+0x136/0x150 net/netfilter/ipvs/ip_vs_dh.c:226
 ip_vs_schedule+0x4cf/0x1000 net/netfilter/ipvs/ip_vs_core.c:527
 udp_conn_schedule+0x230/0x3b0 net/netfilter/ipvs/ip_vs_proto_udp.c:77
 ip_vs_try_to_schedule net/netfilter/ipvs/ip_vs_core.c:1478 [inline]
 ip_vs_in_hook+0x829/0x1520 net/netfilter/ipvs/ip_vs_core.c:2050
 nf_hook_entry_hookfn include/linux/netfilter.h:158 [inline]
 nf_hook_slow+0x78/0x180 net/netfilter/core.c:623
 nf_hook include/linux/netfilter.h:273 [inline]
 __ip_local_out+0x2fd/0x320 net/ipv4/ip_output.c:120
 ip_local_out+0x2a/0xe0 net/ipv4/ip_output.c:129
 iptunnel_xmit+0x3a7/0x500 net/ipv4/ip_tunnel_core.c:84
 udp_tunnel_xmit_skb+0x1aa/0x1f0 net/ipv4/udp_tunnel_core.c:193
 tipc_udp_xmit+0x367/0x440 net/tipc/udp_media.c:198
 tipc_udp_send_msg+0x1b1/0x200 net/tipc/udp_media.c:258
 tipc_bearer_xmit_skb+0x199/0x200 net/tipc/bearer.c:575
 tipc_disc_timeout+0x3fc/0x430 net/tipc/discover.c:338
 call_timer_fn+0x3b/0x280 kernel/time/timer.c:1748
 expire_timers kernel/time/timer.c:1799 [inline]
 __run_timers kernel/time/timer.c:2373 [inline]
 __run_timer_base+0x415/0x610 kernel/time/timer.c:2385
 run_timer_base kernel/time/timer.c:2394 [inline]
 run_timer_softirq+0x31/0x70 kernel/time/timer.c:2404
 handle_softirqs+0xb9/0x280 kernel/softirq.c:622
 __do_softirq kernel/softirq.c:656 [inline]
 invoke_softirq kernel/softirq.c:496 [inline]
 __irq_exit_rcu+0x39/0xc0 kernel/softirq.c:723
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1056 [inline]
 sysvec_apic_timer_interrupt+0x74/0x80 arch/x86/kernel/apic/apic.c:1056
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
 console_flush_one_record arch/x86/include/asm/irqflags.h:-1 [inline]
 console_flush_all+0x540/0x6c0 kernel/printk/printk.c:3289
 __console_flush_and_unlock kernel/printk/printk.c:3319 [inline]
 console_unlock+0xa1/0x280 kernel/printk/printk.c:3359
 vprintk_emit+0x3e4/0x600 kernel/printk/printk.c:2426
 devkmsg_emit+0x7f/0xb0 kernel/printk/printk.c:731
 devkmsg_write+0x1e2/0x2b0 kernel/printk/printk.c:794
 do_iter_readv_writev+0x4fd/0x5a0 fs/read_write.c:-1
 vfs_writev+0x2e1/0x900 fs/read_write.c:1057
 do_writev+0xe9/0x210 fs/read_write.c:1103
 __do_sys_writev fs/read_write.c:1171 [inline]
 __se_sys_writev fs/read_write.c:1168 [inline]
 __x64_sys_writev+0x45/0x50 fs/read_write.c:1168
 x64_sys_call+0x1ba5/0x3000 arch/x86/include/generated/asm/syscalls_64.h:21
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff86a86ba0 of 8 bytes by task 4507 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+0x207/0xae0 kernel/printk/printk_ringbuffer.c:1674
 vprintk_store+0x54a/0x910 kernel/printk/printk.c:2302
 vprintk_emit+0x1a4/0x600 kernel/printk/printk.c:2402
 devkmsg_emit+0x7f/0xb0 kernel/printk/printk.c:731
 devkmsg_write+0x1e2/0x2b0 kernel/printk/printk.c:794
 do_iter_readv_writev+0x4fd/0x5a0 fs/read_write.c:-1
 vfs_writev+0x2e1/0x900 fs/read_write.c:1057
 do_writev+0xe9/0x210 fs/read_write.c:1103
 __do_sys_writev fs/read_write.c:1171 [inline]
 __se_sys_writev fs/read_write.c:1168 [inline]
 __x64_sys_writev+0x45/0x50 fs/read_write.c:1168
 x64_sys_call+0x1ba5/0x3000 arch/x86/include/generated/asm/syscalls_64.h:21
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000000000d1ea8 -> 0x000000000017b708

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 4507 Comm: udevd Tainted: G        W           syzkaller #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
==================================================================
udevd[4507]: symlink '../../loop3' '/dev/disk/by-diskseq/1995.tmp-b7:3' failed: Read-only file system
udevd[4507]: symlink '../../loop3' '/dev/disk/by-diskseq/1995.tmp-b7:3' failed: Read-only file system