==================================================================
BUG: KCSAN: data-race in _prb_read_valid / prb_reserve_in_last

write to 0xffffffff86c6a9d0 of 8 bytes by interrupt on cpu 0:
 data_realloc kernel/printk/printk_ringbuffer.c:1228 [inline]
 prb_reserve_in_last+0x9f1/0xb30 kernel/printk/printk_ringbuffer.c:1495
 vprintk_store+0x457/0x910 kernel/printk/printk.c:2328
 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
 print_daily_error_info+0x28a/0x300 fs/ext4/super.c:3711
 call_timer_fn+0x3b/0x2a0 kernel/time/timer.c:1748
 expire_timers kernel/time/timer.c:1799 [inline]
 __run_timers kernel/time/timer.c:2373 [inline]
 __run_timer_base+0x426/0x620 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+0xb9/0x2a0 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
 __sanitizer_cov_trace_switch+0x6a/0x130 kernel/kcov.c:350
 is_reg64+0x104/0x2b0 kernel/bpf/verifier.c:3831
 __check_reg_arg+0xac/0x230 kernel/bpf/verifier.c:3945
 check_reg_arg kernel/bpf/verifier.c:3979 [inline]
 check_alu_op kernel/bpf/verifier.c:16574 [inline]
 do_check_insn kernel/bpf/verifier.c:21083 [inline]
 do_check+0x74ad/0x9840 kernel/bpf/verifier.c:21352
 do_check_common+0xd0b/0x1630 kernel/bpf/verifier.c:24694
 do_check_main kernel/bpf/verifier.c:24777 [inline]
 bpf_check+0x2f78/0xcc30 kernel/bpf/verifier.c:26100
 bpf_prog_load+0xf76/0x1140 kernel/bpf/syscall.c:3089
 __sys_bpf+0x505/0x7e0 kernel/bpf/syscall.c:6249
 __do_sys_bpf kernel/bpf/syscall.c:6362 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:6360 [inline]
 __x64_sys_bpf+0x41/0x50 kernel/bpf/syscall.c:6360
 x64_sys_call+0x10cb/0x3020 arch/x86/include/generated/asm/syscalls_64.h:322
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff86c6a9c8 of 16 bytes by task 2989 on cpu 1:
 desc_read kernel/printk/printk_ringbuffer.c:496 [inline]
 desc_read_finalized_seq kernel/printk/printk_ringbuffer.c:1931 [inline]
 prb_read kernel/printk/printk_ringbuffer.c:1979 [inline]
 _prb_read_valid+0x1bc/0x950 kernel/printk/printk_ringbuffer.c:2170
 prb_read_valid+0x3c/0x60 kernel/printk/printk_ringbuffer.c:2242
 syslog_print+0x109/0x560 kernel/printk/printk.c:1611
 do_syslog+0x52b/0x7f0 kernel/printk/printk.c:1763
 __do_sys_syslog kernel/printk/printk.c:1855 [inline]
 __se_sys_syslog kernel/printk/printk.c:1853 [inline]
 __x64_sys_syslog+0x41/0x50 kernel/printk/printk.c:1853
 x64_sys_call+0x2b9e/0x3020 arch/x86/include/generated/asm/syscalls_64.h:104
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 2989 Comm: klogd Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
==================================================================