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BUG: KCSAN: data-race in _prb_read_valid / prb_reserve

write to 0xffffffff86ed8368 of 88 bytes by task 2754 on cpu 1:
 prb_reserve+0x6fb/0xaf0 kernel/printk/printk_ringbuffer.c:1693
 vprintk_store+0x54e/0x910 kernel/printk/printk.c:2354
 vprintk_emit+0x1a4/0x610 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
 __ext4_msg+0x1aa/0x1c0 fs/ext4/super.c:1001
 ext4_reconfigure+0xd55/0x1750 fs/ext4/super.c:6929
 reconfigure_super+0x17a/0x5a0 fs/super.c:1143
 do_remount fs/namespace.c:3410 [inline]
 path_mount+0xabd/0xb90 fs/namespace.c:4160
 do_mount fs/namespace.c:4181 [inline]
 __do_sys_mount fs/namespace.c:4397 [inline]
 __se_sys_mount+0x28c/0x2e0 fs/namespace.c:4374
 __x64_sys_mount+0x67/0x80 fs/namespace.c:4374
 x64_sys_call+0xc3b/0x2550 arch/x86/include/generated/asm/syscalls_64.h:166
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x112/0x360 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff86ed8368 of 8 bytes by task 15 on cpu 0:
 desc_read kernel/printk/printk_ringbuffer.c:500 [inline]
 prb_first_seq kernel/printk/printk_ringbuffer.c:2017 [inline]
 _prb_read_valid+0x325/0x930 kernel/printk/printk_ringbuffer.c:2174
 prb_read_valid+0x3c/0x60 kernel/printk/printk_ringbuffer.c:2245
 printk_get_next_message+0xea/0x550 kernel/printk/printk.c:3052
 nbcon_emit_next_record+0x4af/0x1bc0 kernel/printk/nbcon.c:1017
 nbcon_emit_one kernel/printk/nbcon.c:1157 [inline]
 nbcon_kthread_func+0x3fd/0x690 kernel/printk/nbcon.c:1271
 kthread+0x223/0x270 kernel/kthread.c:436
 ret_from_fork+0x146/0x330 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0x0000000000002c57 -> 0x0000000000004c57

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 15 Comm: pr/ttyS0 Not tainted syzkaller #0 PREEMPT(lazy) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
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