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BUG: KCSAN: data-race in _prb_read_valid / data_alloc

write to 0xffffffff86e724f8 of 8 bytes by task 23102 on cpu 0:
 data_alloc+0x2fc/0x380 kernel/printk/printk_ringbuffer.c:1129
 prb_reserve+0x8e3/0xaf0 kernel/printk/printk_ringbuffer.c:1727
 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_check_journal_data_mode+0x82/0x210 fs/ext4/super.c:5060
 __ext4_fill_super fs/ext4/super.c:5430 [inline]
 ext4_fill_super+0x1be3/0x37b0 fs/ext4/super.c:5856
 get_tree_bdev_flags+0x291/0x300 fs/super.c:1872
 get_tree_bdev+0x1f/0x30 fs/super.c:1895
 ext4_get_tree+0x1c/0x30 fs/ext4/super.c:5888
 vfs_get_tree+0x57/0x1d0 fs/super.c:1932
 fc_mount fs/namespace.c:1278 [inline]
 do_new_mount_fc fs/namespace.c:3885 [inline]
 do_new_mount+0x288/0x730 fs/namespace.c:3961
 path_mount+0x4ad/0xb90 fs/namespace.c:4312
 do_mount fs/namespace.c:4325 [inline]
 __do_sys_mount fs/namespace.c:4543 [inline]
 __se_sys_mount+0x28c/0x2e0 fs/namespace.c:4520
 __x64_sys_mount+0x67/0x80 fs/namespace.c:4520
 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 0xffffffff86e724f8 of 16 bytes by task 15 on cpu 1:
 desc_read kernel/printk/printk_ringbuffer.c:496 [inline]
 desc_read_finalized_seq kernel/printk/printk_ringbuffer.c:1934 [inline]
 prb_read kernel/printk/printk_ringbuffer.c:1982 [inline]
 _prb_read_valid+0x183/0x930 kernel/printk/printk_ringbuffer.c:2173
 prb_read_valid+0x3c/0x60 kernel/printk/printk_ringbuffer.c:2245
 nbcon_kthread_should_wakeup kernel/printk/nbcon.c:1207 [inline]
 nbcon_kthread_func+0x1ff/0x690 kernel/printk/nbcon.c:1244
 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

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 15 Comm: pr/ttyS0 Not tainted syzkaller #0 PREEMPT(lazy) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
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