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BUG: KCSAN: data-race in device_del / mm_update_next_owner

write to 0xffff888028c34064 of 4 bytes by task 6272 on cpu 1:
 memalloc_noio_save include/linux/sched/mm.h:197 [inline]
 device_del+0x123/0x9a0 drivers/base/core.c:3087
 device_unregister drivers/base/core.c:3148 [inline]
 device_destroy+0x63/0xa0 drivers/base/core.c:3694
 tty_unregister_device+0x4e/0xd0 drivers/tty/tty_io.c:3190
 gsmld_detach_gsm drivers/tty/n_gsm.c:2407 [inline]
 gsmld_close+0x6c/0x140 drivers/tty/n_gsm.c:2476
 tty_ldisc_close drivers/tty/tty_ldisc.c:488 [inline]
 tty_ldisc_kill drivers/tty/tty_ldisc.c:636 [inline]
 tty_ldisc_release+0x1b6/0x400 drivers/tty/tty_ldisc.c:808
 tty_release_struct+0x19/0xb0 drivers/tty/tty_io.c:1616
 tty_release+0x97b/0x9f0 drivers/tty/tty_io.c:1787
 __fput+0x243/0x4d0 fs/file_table.c:281
 ____fput+0x11/0x20 fs/file_table.c:314
 task_work_run+0x8e/0x110 kernel/task_work.c:151
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:164 [inline]
 exit_to_user_mode_prepare+0x13c/0x170 kernel/entry/common.c:191
 syscall_exit_to_user_mode+0x16/0x30 kernel/entry/common.c:266
 do_syscall_64+0x45/0x80 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888028c34064 of 4 bytes by task 6275 on cpu 0:
 mm_update_next_owner+0x1e9/0x4c0 kernel/exit.c:387
 exit_mm+0x2ff/0x370 kernel/exit.c:485
 do_exit+0x3c2/0x15a0 kernel/exit.c:796
 do_group_exit+0xc8/0x170 kernel/exit.c:906
 get_signal+0xf9b/0x1510 kernel/signal.c:2758
 arch_do_signal+0x25/0x260 arch/x86/kernel/signal.c:811
 exit_to_user_mode_loop kernel/entry/common.c:161 [inline]
 exit_to_user_mode_prepare+0xde/0x170 kernel/entry/common.c:191
 syscall_exit_to_user_mode+0x16/0x30 kernel/entry/common.c:266
 do_syscall_64+0x45/0x80 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 6275 Comm: syz-executor.1 Not tainted 5.10.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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