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    Subjectgeneral protection fault in shmem_unused_huge_count
    From
    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@syzkaller.appspotmail.com

    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 ]---


    ---
    This bug is generated by a bot. It may contain errors.
    See https://goo.gl/tpsmEJ for more information about syzbot.
    syzbot engineers can be reached at syzkaller@googlegroups.com.

    syzbot will keep track of this bug report. See:
    https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with
    syzbot.

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