KCSAN: data-race in do_coredump / do_group_exit

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 8100a580 Merge tag 'x86-urgent-2020-12-06' of git://git.ke..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=130a8c37500000
kernel config: https://syzkaller.appspot.com/x/.config?x=4e0bdb085ef78711
dashboard link: https://syzkaller.appspot.com/bug?extid=28e2b272a4f0906a21f8
compiler: clang version 12.0.0 (https://github.com/llvm/llvm-project.git 913f6005669cfb590c99865a90bc51ed0983d09d)
CC: [linux-...@vger.kernel.org linux-...@vger.kernel.org vi...@zeniv.linux.org.uk]

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

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+28e2b2...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in do_coredump / do_group_exit

write to 0xffff8880273695f4 of 4 bytes by task 920 on cpu 0:
zap_process fs/coredump.c:356 [inline]
zap_threads fs/coredump.c:435 [inline]
coredump_wait fs/coredump.c:462 [inline]
do_coredump+0x4f9/0x1ea0 fs/coredump.c:629
get_signal+0xf65/0x1510 kernel/signal.c:2752
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

read to 0xffff8880273695f4 of 4 bytes by task 923 on cpu 1:
signal_group_exit include/linux/sched/signal.h:268 [inline]
do_group_exit+0x50/0x170 kernel/exit.c:889
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: 1 PID: 923 Comm: syz-executor.4 Not tainted 5.10.0-rc6-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.