KCSAN: data-race in exit_mm / mm_update_next_owner

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 35e884f8 Merge tag 'for-linus-5.8b-rc4-tag' of git://git.k..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=136787e5100000
kernel config: https://syzkaller.appspot.com/x/.config?x=ef2c2e4f6006998c
dashboard link: https://syzkaller.appspot.com/bug?extid=dfcff47717996ec0ac40
compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project.git ca2dcbd030eadbf0aa9b660efe864ff08af6e18b)
CC: [chri...@brauner.io ebie...@xmission.com ja...@google.com linux-...@vger.kernel.org mi...@kernel.org ol...@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+dfcff4...@syzkaller.appspotmail.com

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

write to 0xffff8880b2ba5428 of 8 bytes by task 16835 on cpu 0:
exit_mm+0x292/0x330 kernel/exit.c:477
do_exit+0x415/0x16e0 kernel/exit.c:792
do_group_exit+0xcb/0x180 kernel/exit.c:903
get_signal+0x106d/0x1650 kernel/signal.c:2743
do_signal+0x25/0x270 arch/x86/kernel/signal.c:810
exit_to_usermode_loop arch/x86/entry/common.c:212 [inline]
__prepare_exit_to_usermode+0x127/0x230 arch/x86/entry/common.c:246
__syscall_return_slowpath+0x47/0x60 arch/x86/entry/common.c:329
do_syscall_64+0x5d/0xb0 arch/x86/entry/common.c:368
entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8880b2ba5428 of 8 bytes by task 16830 on cpu 1:
mm_update_next_owner+0x233/0x4a0 kernel/exit.c:389
exit_mm+0x2c0/0x330 kernel/exit.c:481
do_exit+0x415/0x16e0 kernel/exit.c:792
do_group_exit+0x17a/0x180 kernel/exit.c:903
__do_sys_exit_group+0xb/0x10 kernel/exit.c:914
__se_sys_exit_group+0x5/0x10 kernel/exit.c:912
__x64_sys_exit_group+0x16/0x20 kernel/exit.c:912
do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:359
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 16830 Comm: syz-executor.3 Not tainted 5.8.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================


---
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[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: 9f09069cde34 Merge tag 'for-linus' of https://github.com/o..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1259c597f00000
kernel config: https://syzkaller.appspot.com/x/.config?x=c9b534a9d07b6da8
dashboard link: https://syzkaller.appspot.com/bug?extid=dfcff47717996ec0ac40
compiler: Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=134adb48080000
CC: [bra...@kernel.org ebie...@xmission.com kees...@chromium.org linux-...@vger.kernel.org]

IMPORTANT: if you fix the issue, please add the following tag to the commit:

Reported-by: syzbot+dfcff4...@syzkaller.appspotmail.com

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

write to 0xffff88810cfd8ac8 of 8 bytes by task 3690 on cpu 0:
exit_mm+0x98/0x170 kernel/exit.c:503
do_exit+0x51d/0x1720 kernel/exit.c:782
do_group_exit+0xa5/0x160 kernel/exit.c:925
get_signal+0xf54/0x1020 kernel/signal.c:2857
arch_do_signal_or_restart+0x87/0x2d0 arch/x86/kernel/signal.c:869
exit_to_user_mode_loop+0x78/0x130 kernel/entry/common.c:166
exit_to_user_mode_prepare kernel/entry/common.c:201 [inline]
__syscall_exit_to_user_mode_work kernel/entry/common.c:283 [inline]
syscall_exit_to_user_mode+0x6a/0x90 kernel/entry/common.c:294
do_syscall_64+0x37/0x70 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x46/0xb0

read to 0xffff88810cfd8ac8 of 8 bytes by task 3685 on cpu 1:
mm_update_next_owner+0x23c/0x4e0 kernel/exit.c:435
exit_mm+0xd3/0x170 kernel/exit.c:509
do_exit+0x51d/0x1720 kernel/exit.c:782
__x64_sys_exit_group+0x0/0x20 kernel/exit.c:925
__do_sys_exit_group kernel/exit.c:936 [inline]
__se_sys_exit_group kernel/exit.c:934 [inline]
__x64_sys_exit_group+0x1b/0x20 kernel/exit.c:934
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x46/0xb0

value changed: 0xffff88810d585c00 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:

CPU: 1 PID: 3685 Comm: syz-executor.4 Not tainted 5.19.0-rc5-syzkaller-00105-g9f09069cde34-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/29/2022
==================================================================