[syzbot] kernel BUG in collapse_file

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    d6d09a694205 Merge tag 'for-5.14-rc6-tag' of git://git.ker..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14924605300000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f61012d0b1cd846f
dashboard link: https://syzkaller.appspot.com/bug?extid=f17e5ab118d29367bda9
compiler:       Debian clang version 11.0.1-2, GNU ld (GNU Binutils for Debian) 2.35.1

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+f17e5ab118d29367bda9@xxxxxxxxxxxxxxxxxxxxxxxxx

 unmap_region+0x2ab/0x300 mm/mmap.c:2680
 __do_munmap+0x18eb/0x2050 mm/mmap.c:2911
 __do_sys_mremap+0x5d9/0x1390 mm/mremap.c:969
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae
------------[ cut here ]------------
kernel BUG at mm/khugepaged.c:1830!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 1651 Comm: khugepaged Not tainted 5.14.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:collapse_file+0x3537/0x36e0 mm/khugepaged.c:1830
Code: e8 1e 7a b2 ff 48 89 df 48 c7 c6 40 7b 3d 8a e8 ef 02 e8 ff 0f 0b e8 08 7a b2 ff 48 89 df 48 c7 c6 a0 7b 3d 8a e8 d9 02 e8 ff <0f> 0b e8 f2 79 b2 ff 4c 89 e7 48 c7 c6 a0 7e 3d 8a e8 c3 02 e8 ff
RSP: 0018:ffffc900066df820 EFLAGS: 00010046
RAX: 8601299b4ae62f00 RBX: ffffea0000e4e240 RCX: ffff888018fed4c0
RDX: 0000000000000000 RSI: 000000000000ffff RDI: 000000000000ffff
RBP: ffffc900066dfa90 R08: ffffffff81d08764 R09: ffffed1017383f2c
R10: ffffed1017383f2c R11: 0000000000000000 R12: ffffc900066df9d8
R13: dffffc0000000000 R14: ffffc900066dfa20 R15: 0000000000000001
FS:  0000000000000000(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000100000000 CR3: 000000000c48e000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 khugepaged_scan_file mm/khugepaged.c:2051 [inline]
 khugepaged_scan_mm_slot+0x27be/0x2ad0 mm/khugepaged.c:2146
 khugepaged_do_scan+0x2b1/0x640 mm/khugepaged.c:2230
 khugepaged+0x105/0x890 mm/khugepaged.c:2275
 kthread+0x453/0x480 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
Modules linked in:
---[ end trace 8de2a60ea4ac5483 ]---
RIP: 0010:collapse_file+0x3537/0x36e0 mm/khugepaged.c:1830
Code: e8 1e 7a b2 ff 48 89 df 48 c7 c6 40 7b 3d 8a e8 ef 02 e8 ff 0f 0b e8 08 7a b2 ff 48 89 df 48 c7 c6 a0 7b 3d 8a e8 d9 02 e8 ff <0f> 0b e8 f2 79 b2 ff 4c 89 e7 48 c7 c6 a0 7e 3d 8a e8 c3 02 e8 ff
RSP: 0018:ffffc900066df820 EFLAGS: 00010046
RAX: 8601299b4ae62f00 RBX: ffffea0000e4e240 RCX: ffff888018fed4c0
RDX: 0000000000000000 RSI: 000000000000ffff RDI: 000000000000ffff
RBP: ffffc900066dfa90 R08: ffffffff81d08764 R09: ffffed1017383f2c
R10: ffffed1017383f2c R11: 0000000000000000 R12: ffffc900066df9d8
R13: dffffc0000000000 R14: ffffc900066dfa20 R15: 0000000000000001
FS:  0000000000000000(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000100000000 CR3: 000000000c48e000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
   0:	e8 1e 7a b2 ff       	callq  0xffb27a23
   5:	48 89 df             	mov    %rbx,%rdi
   8:	48 c7 c6 40 7b 3d 8a 	mov    $0xffffffff8a3d7b40,%rsi
   f:	e8 ef 02 e8 ff       	callq  0xffe80303
  14:	0f 0b                	ud2    
  16:	e8 08 7a b2 ff       	callq  0xffb27a23
  1b:	48 89 df             	mov    %rbx,%rdi
  1e:	48 c7 c6 a0 7b 3d 8a 	mov    $0xffffffff8a3d7ba0,%rsi
  25:	e8 d9 02 e8 ff       	callq  0xffe80303
  2a:	0f 0b                	ud2     <-- trapping instruction
  2c:	e8 f2 79 b2 ff       	callq  0xffb27a23
  31:	4c 89 e7             	mov    %r12,%rdi
  34:	48 c7 c6 a0 7e 3d 8a 	mov    $0xffffffff8a3d7ea0,%rsi
  3b:	e8 c3 02 e8 ff       	callq  0xffe80303


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