syzbot

pci 0000:00:05.0: vgaarb: VGA decodes changed: olddecodes=io+mem,decodes=none:owns=io+mem
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BUG: KCSAN: data-race in _prb_read_valid / data_alloc

write to 0xffffffff86a6c108 of 8 bytes by task 1647 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
 netif_set_promiscuity+0x39/0x90 net/core/dev.c:9596
 dev_set_promiscuity+0xc1/0x170 net/core/dev_api.c:287
 nbp_delete_promisc net/bridge/br_if.c:254 [inline]
 del_nbp+0xc2/0x720 net/bridge/br_if.c:340
 br_dev_delete+0x4e/0xe0 net/bridge/br_if.c:386
 br_net_exit_rtnl+0x92/0xf0 net/bridge/br.c:414
 ops_exit_rtnl_list net/core/net_namespace.c:181 [inline]
 ops_undo_list+0x1be/0x420 net/core/net_namespace.c:248
 cleanup_net+0x31c/0x550 net/core/net_namespace.c:696
 process_one_work kernel/workqueue.c:3257 [inline]
 process_scheduled_works+0x4cd/0x9d0 kernel/workqueue.c:3340
 worker_thread+0x6bc/0x8b0 kernel/workqueue.c:3421
 kthread+0x488/0x510 kernel/kthread.c:463
 ret_from_fork+0x148/0x280 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

read to 0xffffffff86a6c108 of 16 bytes by task 31833 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
 __console_flush_and_unlock kernel/printk/printk.c:3338 [inline]
 console_unlock+0x146/0x280 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_echoes+0x20d/0x6b0 drivers/tty/n_tty.c:697
 commit_echoes drivers/tty/n_tty.c:750 [inline]
 n_tty_receive_char+0x4bc/0x6d0 drivers/tty/n_tty.c:1413
 n_tty_receive_buf_standard+0x552/0x3f60 drivers/tty/n_tty.c:1582
 __receive_buf drivers/tty/n_tty.c:1616 [inline]
 n_tty_receive_buf_common+0x7f3/0xc10 drivers/tty/n_tty.c:1715
 n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1759
 tty_ldisc_receive_buf+0x66/0xf0 drivers/tty/tty_buffer.c:387
 paste_selection+0x344/0x4a0 drivers/tty/vt/selection.c:439
 tioclinux+0x3b4/0x460 drivers/tty/vt/vt.c:3486
 vt_ioctl+0x75e/0x18d0 drivers/tty/vt/vt_ioctl.c:753
 tty_ioctl+0x7d7/0xb80 drivers/tty/tty_io.c:2792
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xce/0x140 fs/ioctl.c:583
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:583
 x64_sys_call+0x14b0/0x3000 arch/x86/include/generated/asm/syscalls_64.h:17
 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: 31833 Comm: syz.1.11174 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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