syzbot

loop1: detected capacity change from 0 to 2048
EXT4-fs (loop1): mounted filesystem 00000000-0000-0000-0000-000000000000 r/w without journal. Quota mode: none.
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BUG: KCSAN: data-race in n_tty_write / tty_set_termios

write to 0xffff888118108108 of 44 bytes by task 4130 on cpu 0:
 tty_set_termios+0xc0/0x8c0 drivers/tty/tty_ioctl.c:339
 set_termios+0x35b/0x4e0 drivers/tty/tty_ioctl.c:520
 tty_mode_ioctl+0x379/0x5c0 drivers/tty/tty_ioctl.c:-1
 n_tty_ioctl_helper+0x91/0x210 drivers/tty/tty_ioctl.c:986
 n_tty_ioctl+0x101/0x200 drivers/tty/n_tty.c:2509
 tty_ioctl+0x842/0xb80 drivers/tty/tty_io.c:2811
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:906 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:892
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:892
 x64_sys_call+0x19a8/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd0/0x1a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888118108114 of 4 bytes by task 4127 on cpu 1:
 n_tty_write+0x9f/0xb10 drivers/tty/n_tty.c:2354
 iterate_tty_write drivers/tty/tty_io.c:1015 [inline]
 file_tty_write+0x389/0x670 drivers/tty/tty_io.c:1090
 tty_write+0x25/0x30 drivers/tty/tty_io.c:1111
 new_sync_write fs/read_write.c:591 [inline]
 vfs_write+0x49d/0x8d0 fs/read_write.c:684
 ksys_write+0xda/0x1a0 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+0x40/0x50 fs/read_write.c:744
 x64_sys_call+0x2cdd/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd0/0x1a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00008a3b -> 0x00000003

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 4127 Comm: syz.1.210 Not tainted 6.15.0-rc5-syzkaller-00136-g9c69f8884904 #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/19/2025
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