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BUG: KCSAN: data-race in _prb_read_valid / data_alloc

write to 0xffffffff86c7a388 of 8 bytes by task 26439 on cpu 0:
 data_alloc+0x310/0x390 kernel/printk/printk_ringbuffer.c:1129
 prb_reserve+0x8d7/0xae0 kernel/printk/printk_ringbuffer.c:1724
 vprintk_store+0x54a/0x910 kernel/printk/printk.c:2354
 vprintk_emit+0x1a4/0x600 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
 _fat_msg+0xb0/0xe0 fs/fat/misc.c:62
 __fat_fs_error+0x1b3/0x1e0 fs/fat/misc.c:39
 fat_ent_read+0x55d/0x5c0 fs/fat/fatent.c:359
 fat_free_clusters+0x17b/0x8a0 fs/fat/fatent.c:568
 fat_free fs/fat/file.c:377 [inline]
 fat_truncate_blocks+0x510/0x5a0 fs/fat/file.c:395
 fat_setattr+0x78e/0x870 fs/fat/file.c:552
 notify_change+0x872/0x8f0 fs/attr.c:556
 do_truncate+0x14f/0x190 fs/open.c:68
 handle_truncate fs/namei.c:4279 [inline]
 do_open fs/namei.c:4675 [inline]
 path_openat+0x1c97/0x2050 fs/namei.c:4830
 do_file_open+0x16c/0x290 fs/namei.c:4859
 do_sys_openat2+0x94/0x130 fs/open.c:1366
 do_sys_open fs/open.c:1372 [inline]
 __do_sys_open fs/open.c:1380 [inline]
 __se_sys_open fs/open.c:1376 [inline]
 __x64_sys_open+0xe6/0x110 fs/open.c:1376
 x64_sys_call+0x14b9/0x3020 arch/x86/include/generated/asm/syscalls_64.h:3
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff86c7a388 of 16 bytes by task 26444 on cpu 1:
 desc_read kernel/printk/printk_ringbuffer.c:496 [inline]
 desc_read_finalized_seq kernel/printk/printk_ringbuffer.c:1931 [inline]
 prb_read kernel/printk/printk_ringbuffer.c:1979 [inline]
 _prb_read_valid+0x1bc/0x950 kernel/printk/printk_ringbuffer.c:2170
 prb_read_valid+0x3c/0x60 kernel/printk/printk_ringbuffer.c:2242
 printk_get_next_message+0xea/0x560 kernel/printk/printk.c:3052
 console_emit_next_record kernel/printk/printk.c:3137 [inline]
 console_flush_one_record kernel/printk/printk.c:3269 [inline]
 console_flush_all+0x2cd/0x6c0 kernel/printk/printk.c:3343
 __console_flush_and_unlock kernel/printk/printk.c:3373 [inline]
 console_unlock+0xa1/0x280 kernel/printk/printk.c:3413
 class_console_lock_destructor include/linux/console.h:736 [inline]
 con_flush_chars drivers/tty/vt/vt.c:3629 [inline]
 con_write+0xca/0x1d0 drivers/tty/vt/vt.c:3559
 do_output_char+0x49a/0x500 drivers/tty/n_tty.c:418
 process_output drivers/tty/n_tty.c:482 [inline]
 n_tty_write+0x8fe/0xc20 drivers/tty/n_tty.c:2377
 iterate_tty_write drivers/tty/tty_io.c:1006 [inline]
 file_tty_write+0x378/0x690 drivers/tty/tty_io.c:1081
 tty_write+0x25/0x30 drivers/tty/tty_io.c:1102
 do_iter_readv_writev+0x4fd/0x5a0 fs/read_write.c:-1
 vfs_writev+0x2e1/0x900 fs/read_write.c:1059
 do_writev+0xe9/0x210 fs/read_write.c:1105
 __do_sys_writev fs/read_write.c:1173 [inline]
 __se_sys_writev fs/read_write.c:1170 [inline]
 __x64_sys_writev+0x45/0x50 fs/read_write.c:1170
 x64_sys_call+0x1c0c/0x3020 arch/x86/include/generated/asm/syscalls_64.h:21
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 26444 Comm: syz.6.20672 Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
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