KCSAN: data-race in futex_wait_queue_me / mm_update_next_owner (2)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 7c3cd68e Merge remote-tracking branch 'linux-rcu/kcsan' in..
git tree: https://github.com/google/ktsan.git kcsan
console output: https://syzkaller.appspot.com/x/log.txt?x=118e11d6100000
kernel config: https://syzkaller.appspot.com/x/.config?x=ff291dc25f22cdda
dashboard link: https://syzkaller.appspot.com/bug?extid=35e8f1b76e968e1180eb
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
CC: [dvh...@infradead.org linux-...@vger.kernel.org mi...@redhat.com pet...@infradead.org tg...@linutronix.de]

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+35e8f1...@syzkaller.appspotmail.com

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

write to 0xffff8880a19ab0a4 of 4 bytes by task 2024 on cpu 1:
freezer_count include/linux/freezer.h:121 [inline]
freezable_schedule include/linux/freezer.h:173 [inline]
futex_wait_queue_me+0x19e/0x290 kernel/futex.c:2631
futex_wait+0x17e/0x3a0 kernel/futex.c:2737
do_futex+0xe2/0x15b0 kernel/futex.c:3808
__do_sys_futex kernel/futex.c:3869 [inline]
__se_sys_futex kernel/futex.c:3837 [inline]
__x64_sys_futex+0x2dc/0x410 kernel/futex.c:3837
do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8880a19ab0a4 of 4 bytes by task 2026 on cpu 0:
mm_update_next_owner+0x376/0x5a0 kernel/exit.c:383
exit_mm kernel/exit.c:478 [inline]
do_exit+0x63c/0x11e0 kernel/exit.c:782
do_group_exit+0xae/0x1a0 kernel/exit.c:893
get_signal+0x2a7/0x1290 kernel/signal.c:2739
do_signal+0x2b/0x840 arch/x86/kernel/signal.c:784
exit_to_usermode_loop+0x24a/0x2c0 arch/x86/entry/common.c:161
prepare_exit_to_usermode arch/x86/entry/common.c:196 [inline]
syscall_return_slowpath arch/x86/entry/common.c:279 [inline]
do_syscall_64+0x38b/0x3b0 arch/x86/entry/common.c:305
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 2026 Comm: syz-executor.1 Not tainted 5.7.0-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.