KCSAN: data-race in mm_update_next_owner / ns_capable_common

[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=10355c99e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=a38292766f8efdaa
dashboard link: https://syzkaller.appspot.com/bug?extid=18a3ca9fff51570511ff
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+18a3ca...@syzkaller.appspotmail.com

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

read to 0xffff88811d50b064 of 4 bytes by task 19197 on cpu 1:
mm_update_next_owner+0x373/0x5a0 kernel/exit.c:389
exit_mm kernel/exit.c:484 [inline]
do_exit+0x4a4/0x18c0 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

write to 0xffff88811d50b064 of 4 bytes by task 7766 on cpu 0:
ns_capable_common+0x9f/0xc0 kernel/capability.c:377
ns_capable+0x29/0x40 kernel/capability.c:396
netlink_allowed net/netlink/af_netlink.c:912 [inline]
netlink_sendmsg+0x824/0x8b0 net/netlink/af_netlink.c:1871
sock_sendmsg_nosec net/socket.c:639 [inline]
sock_sendmsg+0x9f/0xc0 net/socket.c:659
____sys_sendmsg+0x49d/0x4d0 net/socket.c:2330
___sys_sendmsg+0xb5/0x100 net/socket.c:2384
__sys_sendmsg+0xa0/0x160 net/socket.c:2417
__do_sys_sendmsg net/socket.c:2426 [inline]
__se_sys_sendmsg net/socket.c:2424 [inline]
__x64_sys_sendmsg+0x51/0x70 net/socket.c:2424
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: 7766 Comm: udevd 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.