BUG: KCSAN: data-race in _prb_read_valid / prb_reserve

write to 0xffffffff86938c98 of 88 bytes by task 8381 on cpu 1:
 prb_reserve+0x696/0xaf0 kernel/printk/printk_ringbuffer.c:1635
 vprintk_store+0x56d/0x860 kernel/printk/printk.c:2326
 vprintk_emit+0x178/0x650 kernel/printk/printk.c:2426
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2465
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2475
 printk_stack_address arch/x86/kernel/dumpstack.c:70 [inline]
 show_trace_log_lvl+0x4e3/0x560 arch/x86/kernel/dumpstack.c:282
 __dump_stack+0x1d/0x30 lib/dump_stack.c:94
 dump_stack_lvl+0xe8/0x140 lib/dump_stack.c:120
 dump_stack+0x15/0x1b lib/dump_stack.c:129
 fail_dump lib/fault-inject.c:73 [inline]
 should_fail_ex+0x265/0x280 lib/fault-inject.c:174
 should_fail+0xb/0x20 lib/fault-inject.c:184
 should_fail_usercopy+0x1a/0x20 lib/fault-inject-usercopy.c:37
 _inline_copy_to_user include/linux/uaccess.h:193 [inline]
 _copy_to_user+0x20/0xa0 lib/usercopy.c:26
 copy_to_user include/linux/uaccess.h:225 [inline]
 simple_read_from_buffer+0xb5/0x130 fs/libfs.c:1135
 proc_fail_nth_read+0x10e/0x150 fs/proc/base.c:1488
 vfs_read+0x1a0/0x6f0 fs/read_write.c:570
 ksys_read+0xda/0x1a0 fs/read_write.c:715
 __do_sys_read fs/read_write.c:724 [inline]
 __se_sys_read fs/read_write.c:722 [inline]
 __x64_sys_read+0x40/0x50 fs/read_write.c:722
 x64_sys_call+0x27bc/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:1
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff86938c98 of 8 bytes by task 8379 on cpu 0:
 desc_read kernel/printk/printk_ringbuffer.c:486 [inline]
 prb_first_seq kernel/printk/printk_ringbuffer.c:1957 [inline]
 _prb_read_valid+0x383/0x920 kernel/printk/printk_ringbuffer.c:2114
 prb_read_valid_info+0x66/0x90 kernel/printk/printk_ringbuffer.c:2219
 find_first_fitting_seq+0x1b1/0x320 kernel/printk/printk.c:1589
 syslog_print_all+0x111/0x3a0 kernel/printk/printk.c:1721
 do_syslog+0x2fd/0x7e0 kernel/printk/printk.c:1799
 __do_sys_syslog kernel/printk/printk.c:1877 [inline]
 __se_sys_syslog kernel/printk/printk.c:1875 [inline]
 __x64_sys_syslog+0x41/0x50 kernel/printk/printk.c:1875
 x64_sys_call+0x2f36/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:104
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000007d43 -> 0x0000000000009d43

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 8379 Comm: syz.8.18695 Tainted: G        W           6.16.0-syzkaller-10355-gf2d282e1dfb3 #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
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