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BUG: KCSAN: data-race in pty_close / pty_stop

write to 0xffff888129c06ddc of 2 bytes by task 6171 on cpu 0:
 pty_close+0x14a/0x2d0 drivers/tty/pty.c:61
 tty_release+0x255/0xa10 drivers/tty/tty_io.c:1778
 __fput+0x25b/0x4e0 fs/file_table.c:280
 ____fput+0x11/0x20 fs/file_table.c:313
 task_work_run+0xae/0x130 kernel/task_work.c:164
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:174 [inline]
 exit_to_user_mode_prepare+0x156/0x190 kernel/entry/common.c:208
 __syscall_exit_to_user_mode_work kernel/entry/common.c:290 [inline]
 syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:301
 do_syscall_64+0x56/0x90 arch/x86/entry/common.c:57
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888129c06ddc of 2 bytes by task 6183 on cpu 1:
 pty_stop+0x39/0xf0 drivers/tty/pty.c:362
 __stop_tty drivers/tty/tty_io.c:790 [inline]
 stop_tty drivers/tty/tty_io.c:798 [inline]
 tty_send_xchar+0x1e2/0x290 drivers/tty/tty_io.c:1192
 n_tty_ioctl_helper+0x2a3/0x4c0 drivers/tty/tty_ioctl.c:870
 n_tty_ioctl+0x102/0x200 drivers/tty/n_tty.c:2487
 tty_ioctl+0xa8f/0x1120 drivers/tty/tty_io.c:2814
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:1069 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:1055
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:1055
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x0100 -> 0x0000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 6183 Comm: syz-executor.3 Not tainted 5.13.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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