general protection fault in shmem_unused_huge_count

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    3eb2ce825ea1 Linux 4.16-rc7
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16bd9d93800000
kernel config:  https://syzkaller.appspot.com/x/.config?x=8addcf4530d93e53
dashboard link: https://syzkaller.appspot.com/bug?extid=d2586fde8fdcead3647f
compiler:       gcc (GCC) 7.1.1 20170620

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+d2586fde8fdcead3647f@xxxxxxxxxxxxxxxxxxxxxxxxx

kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 9915 Comm: syz-executor3 Not tainted 4.16.0-rc7+ #3
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:__read_once_size include/linux/compiler.h:188 [inline]
RIP: 0010:shmem_unused_huge_count+0x8e/0x100 mm/shmem.c:561
RSP: 0018:ffff8801b0e9f460 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: 1ffff100361d3e8d RCX: ffffffff8195e5e7
RDX: 0000000000000021 RSI: ffff8801b0e9f778 RDI: 0000000000000108
RBP: ffff8801b0e9f4e0 R08: 0000000000000000 R09: 1ffff100361d3e76
R10: ffff8801b0e9f378 R11: 0000000000000001 R12: 0000000000000000
R13: dffffc0000000000 R14: ffff8801b4c5cdf0 R15: 0000000000000000
FS:  0000000000d5a940(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000d5ac10 CR3: 00000001d8120003 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 super_cache_count+0x96/0x280 fs/super.c:131
 do_shrink_slab mm/vmscan.c:310 [inline]
 shrink_slab.part.46+0x30c/0xe80 mm/vmscan.c:475
 shrink_slab+0x9d/0xb0 mm/vmscan.c:442
 shrink_node+0x51e/0xf70 mm/vmscan.c:2556
 shrink_zones mm/vmscan.c:2728 [inline]
 do_try_to_free_pages+0x383/0x1020 mm/vmscan.c:2790
 try_to_free_mem_cgroup_pages+0x44d/0xb40 mm/vmscan.c:3079
 reclaim_high.constprop.64+0x1e2/0x330 mm/memcontrol.c:1862
 mem_cgroup_handle_over_high+0x8d/0x130 mm/memcontrol.c:1887
 tracehook_notify_resume include/linux/tracehook.h:193 [inline]
 exit_to_usermode_loop+0x242/0x2f0 arch/x86/entry/common.c:166
 prepare_exit_to_usermode arch/x86/entry/common.c:196 [inline]
 syscall_return_slowpath+0x487/0x550 arch/x86/entry/common.c:265
 ret_from_fork+0x15/0x50 arch/x86/entry/entry_64.S:399
RIP: 0033:0x452f5a
RSP: 002b:00007ffdaa5ef700 EFLAGS: 00000246 ORIG_RAX: 0000000000000038
RAX: 0000000000000000 RBX: 00007ffdaa5ef700 RCX: 0000000000452f5a
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000001200011
RBP: 00007ffdaa5ef740 R08: 0000000000000001 R09: 0000000000d5a940
R10: 0000000000d5ac10 R11: 0000000000000246 R12: 0000000000000001
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000001380
Code: c1 e8 03 42 80 3c 28 00 75 6f 4d 8b a4 24 80 06 00 00 48 b8 00 00 00  
00 00 fc ff df 49 8d bc 24 08 01 00 00 48 89 fa 48 c1 ea 03 <80> 3c 02 00  
75 5e 48 8d 7d a8 48 ba 00 00 00 00 00 fc ff df 49
RIP: __read_once_size include/linux/compiler.h:188 [inline] RSP:  
ffff8801b0e9f460
RIP: shmem_unused_huge_count+0x8e/0x100 mm/shmem.c:561 RSP: ffff8801b0e9f460
---[ end trace 8116f40602cb9839 ]---


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