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BUG: KCSAN: data-race in _prb_read_valid / data_alloc

write to 0xffffffff8686a458 of 8 bytes by task 19887 on cpu 1:
 data_alloc+0x274/0x2e0 kernel/printk/printk_ringbuffer.c:1101
 prb_reserve+0x807/0xaf0 kernel/printk/printk_ringbuffer.c:1685
 vprintk_store+0x56d/0x860 kernel/printk/printk.c:2299
 vprintk_emit+0x10d/0x580 kernel/printk/printk.c:2399
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2438
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2448
 __ext4_msg+0x18f/0x1a0 fs/ext4/super.c:990
 ext4_commit_super+0x238/0x280 fs/ext4/super.c:6238
 ext4_handle_error+0x451/0x550 fs/ext4/super.c:718
 __ext4_error_inode+0x1e3/0x3f0 fs/ext4/super.c:861
 ext4_get_inode_loc fs/ext4/inode.c:4969 [inline]
 ext4_reserve_inode_write+0x126/0x250 fs/ext4/inode.c:6294
 __ext4_mark_inode_dirty+0x8c/0x3f0 fs/ext4/inode.c:6472
 ext4_dirty_inode+0x92/0xc0 fs/ext4/inode.c:6509
 __mark_inode_dirty+0x162/0x750 fs/fs-writeback.c:2566
 ext4_mb_new_blocks+0x10b9/0x2080 fs/ext4/mballoc.c:-1
 ext4_ext_map_blocks+0xff5/0x38a0 fs/ext4/extents.c:4383
 ext4_map_create_blocks fs/ext4/inode.c:609 [inline]
 ext4_map_blocks+0x5ee/0xd00 fs/ext4/inode.c:811
 _ext4_get_block+0x10a/0x350 fs/ext4/inode.c:910
 ext4_get_block_unwritten+0x2a/0xb0 fs/ext4/inode.c:943
 ext4_block_write_begin+0x5e8/0xc00 fs/ext4/inode.c:1198
 ext4_write_begin+0x647/0xeb0 fs/ext4/ext4_jbd2.h:-1
 ext4_da_write_begin+0x1fb/0x6e0 fs/ext4/inode.c:3129
 generic_perform_write+0x184/0x490 mm/filemap.c:4242
 ext4_buffered_write_iter+0x1ee/0x3c0 fs/ext4/file.c:299
 ext4_file_write_iter+0x387/0xf60 fs/ext4/file.c:-1
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x52a/0x960 fs/read_write.c:686
 ksys_write+0xda/0x1a0 fs/read_write.c:738
 __do_sys_write fs/read_write.c:749 [inline]
 __se_sys_write fs/read_write.c:746 [inline]
 __x64_sys_write+0x40/0x50 fs/read_write.c:746
 x64_sys_call+0x2802/0x3000 arch/x86/include/generated/asm/syscalls_64.h:2
 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 0xffffffff8686a458 of 16 bytes by task 19902 on cpu 0:
 desc_read kernel/printk/printk_ringbuffer.c:479 [inline]
 desc_read_finalized_seq kernel/printk/printk_ringbuffer.c:1892 [inline]
 prb_read kernel/printk/printk_ringbuffer.c:1940 [inline]
 _prb_read_valid+0x1bc/0x920 kernel/printk/printk_ringbuffer.c:2131
 prb_read_valid+0x3c/0x60 kernel/printk/printk_ringbuffer.c:2203
 __console_flush_and_unlock kernel/printk/printk.c:3277 [inline]
 console_unlock+0x164/0x2e0 kernel/printk/printk.c:3298
 class_console_lock_destructor include/linux/console.h:669 [inline]
 do_con_write+0x28df/0x2940 drivers/tty/vt/vt.c:3243
 con_put_char+0x38/0x60 drivers/tty/vt/vt.c:3573
 tty_put_char+0x68/0xc0 drivers/tty/tty_io.c:3153
 n_tty_process_echo_ops drivers/tty/n_tty.c:608 [inline]
 __process_echoes+0x414/0x6b0 drivers/tty/n_tty.c:693
 flush_echoes drivers/tty/n_tty.c:791 [inline]
 __receive_buf drivers/tty/n_tty.c:1626 [inline]
 n_tty_receive_buf_common+0x8e4/0xbe0 drivers/tty/n_tty.c:1723
 n_tty_receive_buf+0x30/0x40 drivers/tty/n_tty.c:1763
 tiocsti+0x170/0x1d0 drivers/tty/tty_io.c:2290
 tty_ioctl+0x4a4/0xb80 drivers/tty/tty_io.c:2706
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xce/0x140 fs/ioctl.c:583
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:583
 x64_sys_call+0x1816/0x3000 arch/x86/include/generated/asm/syscalls_64.h:17
 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

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 19902 Comm: syz.2.5091 Not tainted syzkaller #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
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