KCSAN: data-race in do_exit / mm_update_next_owner (3)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 245a4300 Merge branch 'rcu/kcsan' into tip/locking/kcsan
git tree: https://github.com/google/ktsan.git kcsan
console output: https://syzkaller.appspot.com/x/log.txt?x=10d811a5e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=a4b9db179318d21f
dashboard link: https://syzkaller.appspot.com/bug?extid=42b1257d28c1eab42d84
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
CC: [chri...@brauner.io ebie...@xmission.com linux-...@vger.kernel.org mi...@kernel.org ol...@redhat.com pet...@infradead.org tg...@linutronix.de el...@google.com]

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+42b125...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in do_exit / mm_update_next_owner

write to 0xffff88812a69a428 of 8 bytes by task 18623 on cpu 1:
exit_mm kernel/exit.c:480 [inline]
do_exit+0x475/0x18c0 kernel/exit.c:784
do_group_exit+0xb4/0x1c0 kernel/exit.c:895
get_signal+0x2a2/0x1320 kernel/signal.c:2734
do_signal+0x2f/0x6c0 arch/x86/kernel/signal.c:815
exit_to_usermode_loop+0x250/0x2c0 arch/x86/entry/common.c:160
prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline]
syscall_return_slowpath arch/x86/entry/common.c:278 [inline]
do_syscall_64+0x384/0x3a0 arch/x86/entry/common.c:304
entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88812a69a428 of 8 bytes by task 18622 on cpu 0:
mm_update_next_owner+0x448/0x5a0 kernel/exit.c:392
exit_mm kernel/exit.c:484 [inline]
do_exit+0x4a4/0x18c0 kernel/exit.c:784
do_group_exit+0xb4/0x1c0 kernel/exit.c:895
__do_sys_exit_group kernel/exit.c:906 [inline]
__se_sys_exit_group kernel/exit.c:904 [inline]
__x64_sys_exit_group+0x2e/0x30 kernel/exit.c:904
do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 18622 Comm: syz-executor.1 Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.