BUG: corrupted list in __khugepaged_exit

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 22fbc037 Merge tag 'for-linus' of git://git.kernel.org/pub..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1455ac3f900000
kernel config: https://syzkaller.appspot.com/x/.config?x=89ab6a0c48f30b49
dashboard link: https://syzkaller.appspot.com/bug?extid=9f87e85f412b739cb154
compiler: gcc (GCC) 10.1.0-syz 20200507
CC: [ak...@linux-foundation.org linux-...@vger.kernel.org linu...@kvack.org]

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+9f87e8...@syzkaller.appspotmail.com

list_del corruption. next->prev should be ffff888049f556f0, but was 0000000000000000
------------[ cut here ]------------
kernel BUG at lib/list_debug.c:54!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 327 Comm: syz-executor.1 Not tainted 5.9.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:__list_del_entry_valid.cold+0x48/0x55 lib/list_debug.c:54
Code: e8 61 8f 9b fd 0f 0b 4c 89 e2 48 89 ee 48 c7 c7 00 b4 d8 88 e8 4d 8f 9b fd 0f 0b 48 89 ee 48 c7 c7 c0 b4 d8 88 e8 3c 8f 9b fd <0f> 0b cc cc cc cc cc cc cc cc cc cc cc 41 57 41 56 41 55 41 54 55
RSP: 0018:ffffc90016f0fae8 EFLAGS: 00010282
RAX: 0000000000000054 RBX: ffffffff8b598ff8 RCX: 0000000000000000
RDX: ffff88809498a280 RSI: ffffffff815f59d5 RDI: fffff52002de1f4f
RBP: ffff888049f556f0 R08: 0000000000000054 R09: ffff8880ae4318e7
R10: 0000000000000000 R11: 0000000000000000 R12: ffff88809a04fd20
R13: ffff8880001570c0 R14: ffff888049f556f8 R15: ffff8880229fea80
FS: 0000000000000000(0000) GS:ffff8880ae400000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b31b23000 CR3: 000000005314c000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
__list_del_entry include/linux/list.h:132 [inline]
list_del include/linux/list.h:146 [inline]
__khugepaged_exit+0x18f/0x3f0 mm/khugepaged.c:521
khugepaged_exit include/linux/khugepaged.h:51 [inline]
__mmput+0x389/0x470 kernel/fork.c:1076
mmput+0x53/0x60 kernel/fork.c:1098
exit_mm kernel/exit.c:483 [inline]
do_exit+0xa8b/0x29f0 kernel/exit.c:793
do_group_exit+0x125/0x310 kernel/exit.c:903
get_signal+0x428/0x1f00 kernel/signal.c:2757
arch_do_signal+0x82/0x2520 arch/x86/kernel/signal.c:811
exit_to_user_mode_loop kernel/entry/common.c:161 [inline]
exit_to_user_mode_prepare+0x1ae/0x200 kernel/entry/common.c:192
syscall_exit_to_user_mode+0x7e/0x2e0 kernel/entry/common.c:267
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45de89
Code: Bad RIP value.
RSP: 002b:00007f134f416cf8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 000000000118bf28 RCX: 000000000045de89
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 000000000118bf28
RBP: 000000000118bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000118bf2c
R13: 000000000169fb6f R14: 00007f134f4179c0 R15: 000000000118bf2c
Modules linked in:
---[ end trace 51b6cd42c4e107c8 ]---
RIP: 0010:__list_del_entry_valid.cold+0x48/0x55 lib/list_debug.c:54
Code: e8 61 8f 9b fd 0f 0b 4c 89 e2 48 89 ee 48 c7 c7 00 b4 d8 88 e8 4d 8f 9b fd 0f 0b 48 89 ee 48 c7 c7 c0 b4 d8 88 e8 3c 8f 9b fd <0f> 0b cc cc cc cc cc cc cc cc cc cc cc 41 57 41 56 41 55 41 54 55
RSP: 0018:ffffc90016f0fae8 EFLAGS: 00010282
RAX: 0000000000000054 RBX: ffffffff8b598ff8 RCX: 0000000000000000
RDX: ffff88809498a280 RSI: ffffffff815f59d5 RDI: fffff52002de1f4f
RBP: ffff888049f556f0 R08: 0000000000000054 R09: ffff8880ae4318e7
R10: 0000000000000000 R11: 0000000000000000 R12: ffff88809a04fd20
R13: ffff8880001570c0 R14: ffff888049f556f8 R15: ffff8880229fea80
FS: 0000000000000000(0000) GS:ffff8880ae400000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b31b23000 CR3: 000000005314c000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


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[syzbot]

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