kernel BUG at mm/mmap.c:LINE!

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    1127b219 Merge tag 'fallthrough-fixes-5.9-rc3' of git://gi..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=136d098e900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=978db74cb30aa994
dashboard link: https://syzkaller.appspot.com/bug?extid=721b657f8f01708b291b
compiler:       gcc (GCC) 10.1.0-syz 20200507

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+721b657f8f01708b291b@xxxxxxxxxxxxxxxxxxxxxxxxx

start_brk 558decf56000 brk 558ded160000 start_stack 7ffd20847a70
arg_start 7ffd20847e89 arg_end 7ffd20847ea4 env_start 7ffd20847ea4 env_end 7ffd20847fdd
binfmt ffffffff89cdcb60 flags 200cd core_state 0000000000000000
ioctx_table 0000000000000000
------------[ cut here ]------------
kernel BUG at mm/mmap.c:427!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 28867 Comm: systemd-udevd Not tainted 5.9.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:validate_mm+0x617/0x800 mm/mmap.c:427
Code: cf f5 cd ff 44 89 e6 bf ff ff ff ff e8 42 f2 cd ff 41 83 fc ff 0f 85 86 1b 01 00 e8 b3 f5 cd ff 48 8b 7c 24 18 e8 d9 59 fc ff <0f> 0b e8 a2 f5 cd ff 48 8b 54 24 28 48 b8 00 00 00 00 00 fc ff df
RSP: 0018:ffffc90015d6fd98 EFLAGS: 00010286
RAX: 000000000000038d RBX: 000000000000004f RCX: 0000000000000000
RDX: ffff8880475ac380 RSI: ffffffff815dafc7 RDI: fffff52002badf52
RBP: 0000000000000000 R08: 000000000000038d R09: ffff8880ae6318e7
R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000001
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
FS:  00007fb1b935a8c0(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffd20959990 CR3: 0000000217691000 CR4: 00000000001526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 remove_vma_list mm/mmap.c:2616 [inline]
 __do_munmap+0x899/0x1170 mm/mmap.c:2869
 __vm_munmap+0xe6/0x180 mm/mmap.c:2889
 __do_sys_munmap mm/mmap.c:2915 [inline]
 __se_sys_munmap mm/mmap.c:2911 [inline]
 __x64_sys_munmap+0x62/0x80 mm/mmap.c:2911
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7fb1b81d66e7
Code: c7 c0 ff ff ff ff eb 8d 48 8b 15 ac 47 2b 00 f7 d8 64 89 02 e9 5b ff ff ff 66 2e 0f 1f 84 00 00 00 00 00 b8 0b 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 81 47 2b 00 f7 d8 64 89 01 48
RSP: 002b:00007ffd20846cd8 EFLAGS: 00000206 ORIG_RAX: 000000000000000b
RAX: ffffffffffffffda RBX: 0000558decf56100 RCX: 00007fb1b81d66e7
RDX: 0000000000000080 RSI: 000000000080ccec RDI: 00007fb1b7064000
RBP: 0000558debda4d18 R08: 0000558decf6a3c0 R09: 0000000000000000
R10: 00000000ffffffff R11: 0000000000000206 R12: 0000558decf560e0
R13: 0000000000000000 R14: 0000000000000003 R15: 000000000000000e
Modules linked in:
---[ end trace 76a00ebdfa09cc52 ]---
RIP: 0010:validate_mm+0x617/0x800 mm/mmap.c:427
Code: cf f5 cd ff 44 89 e6 bf ff ff ff ff e8 42 f2 cd ff 41 83 fc ff 0f 85 86 1b 01 00 e8 b3 f5 cd ff 48 8b 7c 24 18 e8 d9 59 fc ff <0f> 0b e8 a2 f5 cd ff 48 8b 54 24 28 48 b8 00 00 00 00 00 fc ff df
RSP: 0018:ffffc90015d6fd98 EFLAGS: 00010286
RAX: 000000000000038d RBX: 000000000000004f RCX: 0000000000000000
RDX: ffff8880475ac380 RSI: ffffffff815dafc7 RDI: fffff52002badf52
RBP: 0000000000000000 R08: 000000000000038d R09: ffff8880ae6318e7
R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000001
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
FS:  00007fb1b935a8c0(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fad09fed000 CR3: 0000000217691000 CR4: 00000000001526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


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