kernel panic: EXT4-fs (device loop0): panic forced after error

[syzbot <syzbot+a9a45987b8b2daabdc88@syzkaller.appspotmail.com>]

Hello,

syzbot found the following crash on:

HEAD commit:    c1c07416cdd4 Merge tag 'kbuild-fixes-v4.17' of git://git.k..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11a8a07b800000
kernel config:  https://syzkaller.appspot.com/x/.config?x=5a1dc06635c10d27
dashboard link: https://syzkaller.appspot.com/bug?extid=a9a45987b8b2daabdc88
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=164fa297800000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13635c37800000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+a9a45987b8b2daabdc88@syzkaller.appspotmail.com

random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
EXT4-fs error (device loop0): ext4_iget:4756: inode #2: comm  
syz-executor909: root inode unallocated
Kernel panic - not syncing: EXT4-fs (device loop0): panic forced after error

CPU: 1 PID: 4451 Comm: syz-executor909 Not tainted 4.17.0-rc3+ #34
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
  __dump_stack lib/dump_stack.c:77 [inline]
  dump_stack+0x1b9/0x294 lib/dump_stack.c:113
  panic+0x22f/0x4de kernel/panic.c:184
  ext4_handle_error.part.120.cold.128+0x1d/0x1d fs/ext4/super.c:431
  ext4_handle_error fs/ext4/super.c:408 [inline]
  __ext4_error_inode+0x351/0x730 fs/ext4/super.c:494
  ext4_iget+0xe82/0x3dd0 fs/ext4/inode.c:4756
  ext4_fill_super+0x733c/0xd810 fs/ext4/super.c:4208
  mount_bdev+0x30c/0x3e0 fs/super.c:1164
  ext4_mount+0x34/0x40 fs/ext4/super.c:5740
  mount_fs+0xae/0x328 fs/super.c:1267
  vfs_kern_mount.part.34+0xd4/0x4d0 fs/namespace.c:1037
  vfs_kern_mount fs/namespace.c:1027 [inline]
  do_new_mount fs/namespace.c:2518 [inline]
  do_mount+0x564/0x3070 fs/namespace.c:2848
  ksys_mount+0x12d/0x140 fs/namespace.c:3064
  __do_sys_mount fs/namespace.c:3078 [inline]
  __se_sys_mount fs/namespace.c:3075 [inline]
  __x64_sys_mount+0xbe/0x150 fs/namespace.c:3075
  do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x442dda
RSP: 002b:00007ffdadaf1e38 EFLAGS: 00000297 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000442dda
RDX: 0000000020000480 RSI: 0000000020000100 RDI: 00007ffdadaf1e40
RBP: 0000000000000004 R08: 0000000020000440 R09: 000000000000000a
R10: 0000000000000000 R11: 0000000000000297 R12: 0000000000401c40
R13: 0000000000401cd0 R14: 0000000000000000 R15: 0000000000000000
Dumping ftrace buffer:
    (ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..


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