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BUG: KCSAN: data-race in _prb_read_valid / data_alloc

write to 0xffffffff86891f48 of 8 bytes by task 28915 on cpu 0:
 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
 batadv_tt_local_resize_to_mtu+0x17c/0x1c0 net/batman-adv/translation-table.c:3910
 batadv_update_min_mtu+0x194/0x1a0 net/batman-adv/hard-interface.c:653
 batadv_hard_if_event+0x36f/0x1070 net/batman-adv/hard-interface.c:-1
 notifier_call_chain kernel/notifier.c:85 [inline]
 raw_notifier_call_chain+0x6c/0x1b0 kernel/notifier.c:453
 call_netdevice_notifiers_info+0xae/0x100 net/core/dev.c:2230
 call_netdevice_notifiers_mtu net/core/dev.c:2305 [inline]
 netif_set_mtu_ext+0x296/0x370 net/core/dev.c:9591
 netif_set_mtu+0x4a/0xf0 net/core/dev.c:9612
 dev_set_mtu+0xc1/0x170 net/core/dev_api.c:248
 dev_ifsioc+0x474/0xaa0 net/core/dev_ioctl.c:572
 dev_ioctl+0x70a/0x960 net/core/dev_ioctl.c:823
 sock_do_ioctl+0x197/0x220 net/socket.c:1204
 sock_ioctl+0x41b/0x610 net/socket.c:1311
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:907 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:893
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:893
 x64_sys_call+0x19a8/0x2fb0 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

read to 0xffffffff86891f48 of 16 bytes by task 28903 on cpu 1:
 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
 do_output_char+0x49a/0x500 drivers/tty/n_tty.c:422
 process_output drivers/tty/n_tty.c:486 [inline]
 n_tty_write+0x85b/0xb10 drivers/tty/n_tty.c:2388
 iterate_tty_write drivers/tty/tty_io.c:1015 [inline]
 file_tty_write+0x389/0x670 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+0x4a0/0x8e0 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: 1 UID: 0 PID: 28903 Comm: syz.6.39882 Not tainted 6.15.0-syzkaller-10820-gcd2e103d57e5 #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
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