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BUG: KCSAN: data-race in _prb_read_valid / data_alloc

write to 0xffffffff86a76a88 of 8 bytes by task 20750 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:2302
 vprintk_emit+0x1a4/0x600 kernel/printk/printk.c:2402
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2441
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2451
 __netdev_printk+0x310/0x370 net/core/dev.c:12924
 netdev_info+0xa6/0xd0 net/core/dev.c:12971
 __dev_set_promiscuity+0x1fb/0x3f0 net/core/dev.c:9561
 __dev_set_rx_mode+0x113/0x160 net/core/dev.c:-1
 dev_uc_add+0x8d/0xb0 net/core/dev_addr_lists.c:693
 macvlan_open+0x2f1/0x590 drivers/net/macvlan.c:653
 __dev_open+0x321/0x560 net/core/dev.c:1696
 __dev_change_flags+0x13e/0x400 net/core/dev.c:9749
 netif_change_flags+0x5a/0xd0 net/core/dev.c:9812
 do_setlink+0x905/0x2940 net/core/rtnetlink.c:3158
 rtnl_changelink net/core/rtnetlink.c:3776 [inline]
 __rtnl_newlink net/core/rtnetlink.c:3935 [inline]
 rtnl_newlink+0xea4/0x1370 net/core/rtnetlink.c:4072
 rtnetlink_rcv_msg+0x64b/0x720 net/core/rtnetlink.c:6958
 netlink_rcv_skb+0x123/0x220 net/netlink/af_netlink.c:2550
 rtnetlink_rcv+0x1c/0x30 net/core/rtnetlink.c:6985
 netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
 netlink_unicast+0x5c0/0x690 net/netlink/af_netlink.c:1344
 netlink_sendmsg+0x5c8/0x6f0 net/netlink/af_netlink.c:1894
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg+0x145/0x170 net/socket.c:742
 __sys_sendto+0x2b2/0x380 net/socket.c:2206
 __do_sys_sendto net/socket.c:2213 [inline]
 __se_sys_sendto net/socket.c:2209 [inline]
 __x64_sys_sendto+0x76/0x90 net/socket.c:2209
 x64_sys_call+0x29a7/0x3000 arch/x86/include/generated/asm/syscalls_64.h:45
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff86a76a88 of 16 bytes by task 20862 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:2999
 console_emit_next_record kernel/printk/printk.c:3083 [inline]
 console_flush_one_record kernel/printk/printk.c:3215 [inline]
 console_flush_all+0x2cd/0x6c0 kernel/printk/printk.c:3289
 __console_flush_and_unlock kernel/printk/printk.c:3319 [inline]
 console_unlock+0xa1/0x280 kernel/printk/printk.c:3359
 class_console_lock_destructor include/linux/console.h:737 [inline]
 do_con_write+0x29c8/0x2a30 drivers/tty/vt/vt.c:3243
 con_put_char+0x38/0x60 drivers/tty/vt/vt.c:3573
 tty_put_char+0x68/0xc0 drivers/tty/tty_io.c:3153
 do_output_char+0x4de/0x500 drivers/tty/n_tty.c:459
 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
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x5a6/0x9f0 fs/read_write.c:686
 ksys_write+0xdc/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+0x2847/0x3000 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc0/0x2a0 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: 20862 Comm: syz.4.5473 Tainted: G        W           syzkaller #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
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