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BUG: KCSAN: data-race in _prb_read_valid / data_alloc

write to 0xffffffff868832d8 of 8 bytes by task 19074 on cpu 1:
 data_alloc+0x271/0x2b0 kernel/printk/printk_ringbuffer.c:1095
 prb_reserve+0x808/0xaf0 kernel/printk/printk_ringbuffer.c:1669
 vprintk_store+0x56d/0x860 kernel/printk/printk.c:2326
 vprintk_emit+0x178/0x650 kernel/printk/printk.c:2426
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2465
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2475
 dump_stack_print_info+0xee/0x1b0 lib/dump_stack.c:57
 __dump_stack+0x11/0x30 lib/dump_stack.c:93
 dump_stack_lvl+0xe8/0x140 lib/dump_stack.c:120
 dump_stack+0x15/0x1b lib/dump_stack.c:129
 fail_dump lib/fault-inject.c:73 [inline]
 should_fail_ex+0x265/0x280 lib/fault-inject.c:174
 should_failslab+0x8c/0xb0 mm/failslab.c:46
 slab_pre_alloc_hook mm/slub.c:4101 [inline]
 slab_alloc_node mm/slub.c:4177 [inline]
 __kmalloc_cache_noprof+0x4c/0x320 mm/slub.c:4354
 kmalloc_noprof include/linux/slab.h:905 [inline]
 alloc_name mm/memfd.c:400 [inline]
 __do_sys_memfd_create mm/memfd.c:471 [inline]
 __se_sys_memfd_create+0x1cc/0x590 mm/memfd.c:459
 __x64_sys_memfd_create+0x31/0x40 mm/memfd.c:459
 x64_sys_call+0x122f/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:320
 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 0xffffffff868832d8 of 16 bytes by task 19056 on cpu 0:
 desc_read kernel/printk/printk_ringbuffer.c:482 [inline]
 desc_read_finalized_seq kernel/printk/printk_ringbuffer.c:1874 [inline]
 prb_read kernel/printk/printk_ringbuffer.c:1922 [inline]
 _prb_read_valid+0x1bc/0x920 kernel/printk/printk_ringbuffer.c:2113
 prb_read_valid+0x3c/0x60 kernel/printk/printk_ringbuffer.c:2185
 printk_get_next_message+0xc8/0x510 kernel/printk/printk.c:3005
 console_emit_next_record kernel/printk/printk.c:3092 [inline]
 console_flush_all+0x290/0x730 kernel/printk/printk.c:3226
 __console_flush_and_unlock kernel/printk/printk.c:3285 [inline]
 console_unlock+0xa1/0x330 kernel/printk/printk.c:3325
 con_flush_chars+0xb2/0x1b0 drivers/tty/vt/vt.c:3503
 con_write+0x2e/0x40 drivers/tty/vt/vt.c:3433
 process_output_block drivers/tty/n_tty.c:561 [inline]
 n_tty_write+0x7db/0xb10 drivers/tty/n_tty.c:2377
 iterate_tty_write drivers/tty/tty_io.c:1015 [inline]
 file_tty_write+0x38c/0x670 drivers/tty/tty_io.c:1090
 tty_write+0x25/0x30 drivers/tty/tty_io.c:1111
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x49d/0x8e0 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+0x2cdd/0x2fb0 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

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 19056 Comm: syz.4.3837 Not tainted 6.15.0-syzkaller-12141-gec7714e49479 #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
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