syzbot

incfs: Backing dir is not set, filesystem can't be mounted.
kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 299 Comm: syz-executor159 Not tainted 5.4.161-syzkaller-00026-g8a3679a75730 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:incfs_kill_sb+0x47/0xe0 fs/incfs/vfs.c:1882
Code: 9e f0 03 00 00 48 89 d8 48 c1 e8 03 42 80 3c 28 00 74 08 48 89 df e8 68 32 b2 ff 4c 8b 23 49 8d 5c 24 10 48 89 d8 48 c1 e8 03 <42> 80 3c 28 00 74 08 48 89 df e8 4a 32 b2 ff 48 8b 1b 48 83 c3 30
RSP: 0018:ffff8881de56fcb8 EFLAGS: 00010202
RAX: 0000000000000002 RBX: 0000000000000010 RCX: ffff8881de566e40
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff8881de57e000
RBP: 0000000000000000 R08: ffffffff821f6354 R09: ffffed103bcadf1c
R10: ffffed103bcadf1c R11: 0000000000000000 R12: 0000000000000000
R13: dffffc0000000000 R14: ffff8881de57e000 R15: dffffc0000000000
FS:  0000555557376300(0000) GS:ffff8881f6f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffcc5936080 CR3: 00000001dea71000 CR4: 00000000003406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 deactivate_locked_super+0xaf/0x100 fs/super.c:335
 incfs_mount_fs+0x70c/0x7d0 fs/incfs/vfs.c:1846
 legacy_get_tree+0xde/0x170 fs/fs_context.c:647
 vfs_get_tree+0x83/0x260 fs/super.c:1547
 do_new_mount fs/namespace.c:2843 [inline]
 do_mount+0x17be/0x2390 fs/namespace.c:3163
 ksys_mount+0xc2/0xf0 fs/namespace.c:3372
 __do_sys_mount fs/namespace.c:3386 [inline]
 __se_sys_mount fs/namespace.c:3383 [inline]
 __x64_sys_mount+0xb1/0xc0 fs/namespace.c:3383
 do_syscall_64+0xcb/0x1e0 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7f1cd70cbd29
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 b1 14 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffcc58db318 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0030656c69662f2e RCX: 00007f1cd70cbd29
RDX: 0000000020000000 RSI: 0000000020000040 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 00007ffcc58db4b8
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f1cd708f5b0
R13: 431bde82d7b634db R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
---[ end trace c696e636ecbe7097 ]---
RIP: 0010:incfs_kill_sb+0x47/0xe0 fs/incfs/vfs.c:1882
Code: 9e f0 03 00 00 48 89 d8 48 c1 e8 03 42 80 3c 28 00 74 08 48 89 df e8 68 32 b2 ff 4c 8b 23 49 8d 5c 24 10 48 89 d8 48 c1 e8 03 <42> 80 3c 28 00 74 08 48 89 df e8 4a 32 b2 ff 48 8b 1b 48 83 c3 30
RSP: 0018:ffff8881de56fcb8 EFLAGS: 00010202
RAX: 0000000000000002 RBX: 0000000000000010 RCX: ffff8881de566e40
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff8881de57e000
RBP: 0000000000000000 R08: ffffffff821f6354 R09: ffffed103bcadf1c
R10: ffffed103bcadf1c R11: 0000000000000000 R12: 0000000000000000
R13: dffffc0000000000 R14: ffff8881de57e000 R15: dffffc0000000000
FS:  0000555557376300(0000) GS:ffff8881f6f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffcc5936080 CR3: 00000001dea71000 CR4: 00000000003406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
   0:	9e                   	sahf
   1:	f0 03 00             	lock add (%rax),%eax
   4:	00 48 89             	add    %cl,-0x77(%rax)
   7:	d8 48 c1             	fmuls  -0x3f(%rax)
   a:	e8 03 42 80 3c       	callq  0x3c804212
   f:	28 00                	sub    %al,(%rax)
  11:	74 08                	je     0x1b
  13:	48 89 df             	mov    %rbx,%rdi
  16:	e8 68 32 b2 ff       	callq  0xffb23283
  1b:	4c 8b 23             	mov    (%rbx),%r12
  1e:	49 8d 5c 24 10       	lea    0x10(%r12),%rbx
  23:	48 89 d8             	mov    %rbx,%rax
  26:	48 c1 e8 03          	shr    $0x3,%rax
* 2a:	42 80 3c 28 00       	cmpb   $0x0,(%rax,%r13,1) <-- trapping instruction
  2f:	74 08                	je     0x39
  31:	48 89 df             	mov    %rbx,%rdi
  34:	e8 4a 32 b2 ff       	callq  0xffb23283
  39:	48 8b 1b             	mov    (%rbx),%rbx
  3c:	48 83 c3 30          	add    $0x30,%rbx