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BUG: KCSAN: data-race in memchr / string

write to 0xffffffff883fed15 of 1 bytes by task 29 on cpu 0:
 string_nocheck lib/vsprintf.c:650 [inline]
 string+0x16c/0x210 lib/vsprintf.c:728
 vsnprintf+0xa09/0xe30 lib/vsprintf.c:2824
 vscnprintf+0x42/0x90 lib/vsprintf.c:2930
 printk_sprint+0x30/0x2d0 kernel/printk/printk.c:2165
 vprintk_store+0x570/0x810 kernel/printk/printk.c:2279
 vprintk_emit+0x10c/0x5e0 kernel/printk/printk.c:2329
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2363
 vprintk+0x75/0x80 kernel/printk/printk_safe.c:45
 _printk+0x7a/0xa0 kernel/printk/printk.c:2373
 kauditd_printk_skb kernel/audit.c:546 [inline]
 kauditd_hold_skb+0x1a1/0x1b0 kernel/audit.c:581
 kauditd_send_queue+0x288/0x2e0 kernel/audit.c:766
 kauditd_thread+0x42a/0x650 kernel/audit.c:890
 kthread+0x1d1/0x210 kernel/kthread.c:389
 ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

read to 0xffffffff883fed15 of 1 bytes by task 14053 on cpu 1:
 memchr+0x2a/0x50 lib/string.c:791
 count_lines kernel/printk/printk_ringbuffer.c:1797 [inline]
 copy_data kernel/printk/printk_ringbuffer.c:1843 [inline]
 prb_read kernel/printk/printk_ringbuffer.c:1936 [inline]
 _prb_read_valid+0xa26/0xba0 kernel/printk/printk_ringbuffer.c:2113
 prb_read_valid_info+0x67/0x90 kernel/printk/printk_ringbuffer.c:2216
 find_first_fitting_seq+0x1bc/0x310 kernel/printk/printk.c:1538
 syslog_print_all+0x11d/0x5a0 kernel/printk/printk.c:1670
 do_syslog+0x41c/0x7d0 kernel/printk/printk.c:1748
 __do_sys_syslog kernel/printk/printk.c:1826 [inline]
 __se_sys_syslog kernel/printk/printk.c:1824 [inline]
 __x64_sys_syslog+0x43/0x50 kernel/printk/printk.c:1824
 x64_sys_call+0x26cd/0x2d70 arch/x86/include/generated/asm/syscalls_64.h:104
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x74 -> 0x2f

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 14053 Comm: syz.1.3211 Not tainted 6.10.0-rc7-syzkaller-00141-g43db1e03c086 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024
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