==================================================================
BUG: KCSAN: data-race in _prb_read_valid / prb_reserve

write to 0xffffffff868a63c0 of 8 bytes by task 12280 on cpu 1:
 prb_reserve+0x750/0xb80 kernel/printk/printk_ringbuffer.c:-1
 vprintk_store+0x552/0x860 kernel/printk/printk.c:2326
 vprintk_emit+0x1a0/0x6c0 kernel/printk/printk.c:2426
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2465
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x7f/0xb0 kernel/printk/printk.c:2475
 __ext4_error+0x259/0x340 fs/ext4/super.c:817
 ext4_mb_mark_diskspace_used+0x276/0x3c0 fs/ext4/mballoc.c:4114
 ext4_mb_new_blocks+0xa8d/0x2020 fs/ext4/mballoc.c:6235
 ext4_ext_map_blocks+0x106c/0x36a0 fs/ext4/extents.c:4379
 ext4_map_create_blocks fs/ext4/inode.c:519 [inline]
 ext4_map_blocks+0x5f8/0xdf0 fs/ext4/inode.c:705
 ext4_alloc_file_blocks+0x284/0x730 fs/ext4/extents.c:4520
 ext4_do_fallocate fs/ext4/extents.c:4694 [inline]
 ext4_fallocate+0x3ae/0x690 fs/ext4/extents.c:4750
 vfs_fallocate+0x368/0x3b0 fs/open.c:338
 ksys_fallocate fs/open.c:362 [inline]
 __do_sys_fallocate fs/open.c:367 [inline]
 __se_sys_fallocate fs/open.c:365 [inline]
 __x64_sys_fallocate+0x78/0xc0 fs/open.c:365
 x64_sys_call+0x295f/0x2e10 arch/x86/include/generated/asm/syscalls_64.h:286
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff868a63c0 of 8 bytes by task 12273 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+0x471/0x710 kernel/printk/printk_ringbuffer.c:2114
 prb_read_valid+0x42/0x70 kernel/printk/printk_ringbuffer.c:2185
 printk_get_next_message+0xdc/0x530 kernel/printk/printk.c:3005
 console_emit_next_record kernel/printk/printk.c:3092 [inline]
 console_flush_all+0x2a9/0x7a0 kernel/printk/printk.c:3226
 __console_flush_and_unlock kernel/printk/printk.c:3285 [inline]
 console_unlock+0xf4/0x350 kernel/printk/printk.c:3325
 con_flush_chars+0xb0/0x1b0 drivers/tty/vt/vt.c:3503
 con_write+0x30/0x40 drivers/tty/vt/vt.c:3433
 process_output_block drivers/tty/n_tty.c:574 [inline]
 n_tty_write+0x844/0xb80 drivers/tty/n_tty.c:2389
 iterate_tty_write drivers/tty/tty_io.c:1015 [inline]
 file_tty_write+0x382/0x6a0 drivers/tty/tty_io.c:1090
 tty_write+0x28/0x30 drivers/tty/tty_io.c:1111
 new_sync_write fs/read_write.c:591 [inline]
 vfs_write+0x79b/0x950 fs/read_write.c:684
 ksys_write+0xeb/0x1b0 fs/read_write.c:736
 __do_sys_write fs/read_write.c:747 [inline]
 __se_sys_write fs/read_write.c:744 [inline]
 __x64_sys_write+0x42/0x50 fs/read_write.c:744
 x64_sys_call+0x2a45/0x2e10 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x000000000000024a -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 12273 Comm: syz.1.2722 Not tainted 6.14.0-syzkaller-12508-g92b71befc349 #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
==================================================================
EXT4-fs (loop1): pa ffff8881065f8e00: logic 16, phys. 129, len 24
EXT4-fs error (device loop1): ext4_mb_release_inode_pa:5366: group 0, free 0, pa_free 8