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BUG: KCSAN: data-race in n_tty_receive_char / n_tty_write

write to 0xffffc90000e68028 of 8 bytes by task 21639 on cpu 0:
 commit_echoes drivers/tty/n_tty.c:742 [inline]
 n_tty_receive_char+0x4dd/0x6a0 drivers/tty/n_tty.c:1421
 n_tty_receive_buf_standard+0x4c0/0x2f00 drivers/tty/n_tty.c:1590
 __receive_buf drivers/tty/n_tty.c:1624 [inline]
 n_tty_receive_buf_common+0x837/0xbe0 drivers/tty/n_tty.c:1723
 n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1769
 tty_ldisc_receive_buf+0x63/0x100 drivers/tty/tty_buffer.c:387
 tty_port_default_receive_buf+0x59/0x90 drivers/tty/tty_port.c:37
 receive_buf drivers/tty/tty_buffer.c:445 [inline]
 flush_to_ldisc+0x1d1/0x410 drivers/tty/tty_buffer.c:495
 process_one_work kernel/workqueue.c:3238 [inline]
 process_scheduled_works+0x4de/0xa20 kernel/workqueue.c:3319
 worker_thread+0x52c/0x710 kernel/workqueue.c:3400
 kthread+0x4b7/0x540 kernel/kthread.c:464
 ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:153
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffffc90000e68028 of 8 bytes by task 22661 on cpu 1:
 process_echoes drivers/tty/n_tty.c:768 [inline]
 n_tty_write+0x16c/0xb20 drivers/tty/n_tty.c:2363
 iterate_tty_write drivers/tty/tty_io.c:1015 [inline]
 file_tty_write+0x382/0x6a0 drivers/tty/tty_io.c:1090
 tty_write+0x28/0x30 drivers/tty/tty_io.c:1111
 new_sync_write fs/read_write.c:591 [inline]
 vfs_write+0x79b/0x950 fs/read_write.c:684
 ksys_write+0xeb/0x1b0 fs/read_write.c:736
 __do_sys_write fs/read_write.c:747 [inline]
 __se_sys_write fs/read_write.c:744 [inline]
 __x64_sys_write+0x42/0x50 fs/read_write.c:744
 x64_sys_call+0x2a45/0x2e10 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc9/0x1a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000000004 -> 0x0000000000000008

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 22661 Comm: syz.7.5777 Not tainted 6.15.0-rc2-syzkaller-00471-g119009db2674 #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
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netem: change failed