syzbot

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BUG: KCSAN: data-race in n_tty_lookahead_flow_ctrl / tty_set_termios

write to 0xffff88814aa6b108 of 44 bytes by task 9329 on cpu 1:
 tty_set_termios+0xc0/0x910 drivers/tty/tty_ioctl.c:335
 set_termios+0x373/0x4f0 drivers/tty/tty_ioctl.c:516
 tty_mode_ioctl+0x37f/0x5b0 drivers/tty/tty_ioctl.c:-1
 ppp_synctty_ioctl+0x13f/0x2b0 drivers/net/ppp/ppp_synctty.c:315
 tty_ioctl+0x83e/0xb80 drivers/tty/tty_io.c:2801
 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+0x1563/0x3020 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88814aa6b121 of 1 bytes by task 9200 on cpu 0:
 n_tty_is_char_flow_ctrl drivers/tty/n_tty.c:1196 [inline]
 n_tty_receive_char_flow_ctrl drivers/tty/n_tty.c:1217 [inline]
 n_tty_lookahead_flow_ctrl+0x126/0x300 drivers/tty/n_tty.c:1492
 tty_port_default_lookahead_buf+0x91/0xc0 drivers/tty/tty_port.c:59
 lookahead_bufs drivers/tty/tty_buffer.c:428 [inline]
 flush_to_ldisc+0x288/0x340 drivers/tty/tty_buffer.c:498
 process_one_work kernel/workqueue.c:3275 [inline]
 process_scheduled_works+0x4de/0x9e0 kernel/workqueue.c:3358
 worker_thread+0x581/0x770 kernel/workqueue.c:3439
 kthread+0x22a/0x280 kernel/kthread.c:467
 ret_from_fork+0x150/0x360 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0x11 -> 0x3a

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 9200 Comm: kworker/u8:20 Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Workqueue: events_unbound flush_to_ldisc
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smc: removing ib device syz0