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BUG: KCSAN: data-race in _prb_read_valid / data_alloc

write to 0xffffffff86c91370 of 8 bytes by task 4207 on cpu 1:
 data_alloc+0x310/0x390 kernel/printk/printk_ringbuffer.c:1129
 prb_reserve+0x8d6/0xad0 kernel/printk/printk_ringbuffer.c:1727
 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
 __netdev_printk+0x310/0x370 net/core/dev.c:12949
 netdev_info+0xa6/0xd0 net/core/dev.c:12996
 __dev_set_promiscuity+0x1ee/0x3d0 net/core/dev.c:9618
 netif_set_promiscuity+0x39/0x90 net/core/dev.c:9645
 dev_set_promiscuity+0xc1/0x180 net/core/dev_api.c:288
 packet_dev_mc net/packet/af_packet.c:3651 [inline]
 packet_mc_add+0x39f/0x540 net/packet/af_packet.c:3728
 packet_setsockopt+0xa48/0xfd0 net/packet/af_packet.c:3813
 do_sock_setsockopt net/socket.c:2381 [inline]
 __sys_setsockopt+0x184/0x200 net/socket.c:2406
 __do_sys_setsockopt net/socket.c:2412 [inline]
 __se_sys_setsockopt net/socket.c:2409 [inline]
 __x64_sys_setsockopt+0x64/0x80 net/socket.c:2409
 x64_sys_call+0x2327/0x3020 arch/x86/include/generated/asm/syscalls_64.h:55
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff86c91370 of 16 bytes by task 4197 on cpu 0:
 desc_read kernel/printk/printk_ringbuffer.c:496 [inline]
 desc_read_finalized_seq kernel/printk/printk_ringbuffer.c:1934 [inline]
 prb_read kernel/printk/printk_ringbuffer.c:1982 [inline]
 _prb_read_valid+0x1b6/0x950 kernel/printk/printk_ringbuffer.c:2173
 prb_read_valid+0x3c/0x60 kernel/printk/printk_ringbuffer.c:2245
 __console_flush_and_unlock kernel/printk/printk.c:3392 [inline]
 console_unlock+0x146/0x280 kernel/printk/printk.c:3413
 class_console_lock_destructor include/linux/console.h:736 [inline]
 con_flush_chars drivers/tty/vt/vt.c:3731 [inline]
 con_write+0xca/0x1d0 drivers/tty/vt/vt.c:3661
 process_output_block drivers/tty/n_tty.c:557 [inline]
 n_tty_write+0x826/0xb80 drivers/tty/n_tty.c:2366
 iterate_tty_write drivers/tty/tty_io.c:1006 [inline]
 file_tty_write+0x378/0x680 drivers/tty/tty_io.c:1081
 tty_write+0x25/0x30 drivers/tty/tty_io.c:1102
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x5a6/0x9f0 fs/read_write.c:688
 ksys_write+0xdc/0x1a0 fs/read_write.c:740
 __do_sys_write fs/read_write.c:751 [inline]
 __se_sys_write fs/read_write.c:748 [inline]
 __x64_sys_write+0x40/0x50 fs/read_write.c:748
 x64_sys_call+0x27e1/0x3020 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x3b0 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: 4197 Comm: syz.6.6599 Tainted: G        W           syzkaller #0 PREEMPT(lazy) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
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