BUG: KCSAN: data-race in data_alloc / prb_reserve

write to 0xffffffff8687c468 of 8 bytes by task 11105 on cpu 0:
 data_alloc+0x27d/0x2b0 kernel/printk/printk_ringbuffer.c:1096
 prb_reserve+0x808/0xaf0 kernel/printk/printk_ringbuffer.c:1669
 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
 strncpy_from_user+0x25/0x230 lib/strncpy_from_user.c:118
 getname_flags+0xae/0x3b0 fs/namei.c:157
 getname include/linux/fs.h:2918 [inline]
 __do_sys_unlink fs/namei.c:4696 [inline]
 __se_sys_unlink fs/namei.c:4694 [inline]
 __x64_sys_unlink+0x21/0x40 fs/namei.c:4694
 x64_sys_call+0x2dc0/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:88
 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 0xffffffff8687c468 of 8 bytes by task 11107 on cpu 1:
 desc_read kernel/printk/printk_ringbuffer.c:482 [inline]
 desc_push_tail kernel/printk/printk_ringbuffer.c:778 [inline]
 desc_reserve kernel/printk/printk_ringbuffer.c:924 [inline]
 prb_reserve+0x221/0xaf0 kernel/printk/printk_ringbuffer.c:1619
 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
 fail_dump lib/fault-inject.c:66 [inline]
 should_fail_ex+0x24d/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_from_user include/linux/uaccess.h:163 [inline]
 _copy_from_user+0x1c/0xb0 lib/usercopy.c:18
 copy_from_user include/linux/uaccess.h:212 [inline]
 __io_sqe_buffers_update io_uring/rsrc.c:315 [inline]
 __io_register_rsrc_update+0x268/0xac0 io_uring/rsrc.c:360
 io_register_rsrc_update+0x10a/0x120 io_uring/rsrc.c:391
 __io_uring_register io_uring/register.c:739 [inline]
 __do_sys_io_uring_register io_uring/register.c:929 [inline]
 __se_sys_io_uring_register+0x6d9/0xeb0 io_uring/register.c:906
 __x64_sys_io_uring_register+0x55/0x70 io_uring/register.c:906
 x64_sys_call+0x18a3/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:428
 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: 0x000000000013ff70 -> 0x00000000001da178

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 11107 Comm: syz.9.13299 Tainted: G        W           6.16.0-syzkaller-11105-ga6923c06a3b2 #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
==================================================================
FAULT_INJECTION: forcing a failure.
name fail_usercopy, interval 1, probability 0, space 0, times 0
CPU: 1 UID: 0 PID: 11107 Comm: syz.9.13299 Tainted: G        W           6.16.0-syzkaller-11105-ga6923c06a3b2 #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
 <TASK>
 __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_from_user include/linux/uaccess.h:163 [inline]
 _copy_from_user+0x1c/0xb0 lib/usercopy.c:18
 copy_from_user include/linux/uaccess.h:212 [inline]
 __io_sqe_buffers_update io_uring/rsrc.c:315 [inline]
 __io_register_rsrc_update+0x268/0xac0 io_uring/rsrc.c:360
 io_register_rsrc_update+0x10a/0x120 io_uring/rsrc.c:391
 __io_uring_register io_uring/register.c:739 [inline]
 __do_sys_io_uring_register io_uring/register.c:929 [inline]
 __se_sys_io_uring_register+0x6d9/0xeb0 io_uring/register.c:906
 __x64_sys_io_uring_register+0x55/0x70 io_uring/register.c:906
 x64_sys_call+0x18a3/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:428
 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
RIP: 0033:0x7f0d5766eb69
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f0d55ccf038 EFLAGS: 00000246 ORIG_RAX: 00000000000001ab
RAX: ffffffffffffffda RBX: 00007f0d57895fa0 RCX: 00007f0d5766eb69
RDX: 0000200000000240 RSI: 0000000000000010 RDI: 0000000000000005
RBP: 00007f0d55ccf090 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000020 R11: 0000000000000246 R12: 0000000000000001
R13: 0000000000000000 R14: 00007f0d57895fa0 R15: 00007ffe41ad9948
 </TASK>