BUG: unable to handle kernel NULL pointer dereference at 0000000000000020
IP: refcount_dec_and_test arch/x86/include/asm/refcount.h:75 [inline]
IP: vb2_vmalloc_put+0x9/0x60 drivers/media/v4l2-core/videobuf2-vmalloc.c:68
PGD 9cc8c067 P4D 9cc8c067 PUD 9d25b067 PMD 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
Modules linked in:
CPU: 0 PID: 10064 Comm: syz-executor.4 Not tainted 4.14.272-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff88805604a180 task.stack: ffff888056290000
RIP: 0010:refcount_dec_and_test arch/x86/include/asm/refcount.h:75 [inline]
RIP: 0010:vb2_vmalloc_put+0x9/0x60 drivers/media/v4l2-core/videobuf2-vmalloc.c:68
RSP: 0018:ffff888056297ca8 EFLAGS: 00010297
RAX: ffff88805604a180 RBX: ffff88809a330300 RCX: 1ffff1100ac0954a
RDX: 0000000000000000 RSI: ffff88805604aa30 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: ffff88809a330314 R14: 0000000000000000 R15: ffffffff84c25ba0
FS:  00005555555f3400(0000) GS:ffff8880ba400000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000020 CR3: 000000009cf90000 CR4: 00000000003406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 __vb2_buf_mem_free+0xfa/0x1d0 drivers/media/v4l2-core/videobuf2-core.c:240
 __vb2_free_mem drivers/media/v4l2-core/videobuf2-core.c:409 [inline]
 __vb2_queue_free+0x60d/0x7a0 drivers/media/v4l2-core/videobuf2-core.c:454
 vb2_core_queue_release+0x5b/0x70 drivers/media/v4l2-core/videobuf2-core.c:2054
 v4l2_m2m_ctx_release+0x1a/0x30 drivers/media/v4l2-core/v4l2-mem2mem.c:673
 vim2m_release+0xd4/0x120 drivers/media/platform/vim2m.c:959
 v4l2_release+0xf4/0x190 drivers/media/v4l2-core/v4l2-dev.c:446
 __fput+0x25f/0x7a0 fs/file_table.c:210
 task_work_run+0x11f/0x190 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:191 [inline]
 exit_to_usermode_loop+0x1ad/0x200 arch/x86/entry/common.c:164
 prepare_exit_to_usermode arch/x86/entry/common.c:199 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:270 [inline]
 do_syscall_64+0x4a3/0x640 arch/x86/entry/common.c:297
 entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x7f6b97e9fc8b
RSP: 002b:00007ffea08ff490 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000004 RCX: 00007f6b97e9fc8b
RDX: 00007f6b98004478 RSI: ffffffffffffffff RDI: 0000000000000003
RBP: 00007f6b98001960 R08: 0000000000000000 R09: 00007f6b98004480
R10: 00007ffea08ff590 R11: 0000000000000293 R12: 00000000000441d7
R13: 00007ffea08ff590 R14: 00007f6b97ffff60 R15: 0000000000000032
Code: e9 ca fc ff ff e8 a8 97 bc fc e9 96 fc ff ff e8 ce 99 bc fc e9 fd fe ff ff 66 0f 1f 84 00 00 00 00 00 55 48 89 fd e8 97 e6 92 fc <f0> ff 4d 20 0f 88 a7 6f 5f 02 74 06 5d e9 85 e6 92 fc e8 80 e6 
RIP: refcount_dec_and_test arch/x86/include/asm/refcount.h:75 [inline] RSP: ffff888056297ca8
RIP: vb2_vmalloc_put+0x9/0x60 drivers/media/v4l2-core/videobuf2-vmalloc.c:68 RSP: ffff888056297ca8
CR2: 0000000000000020
---[ end trace dd38222caa079cac ]---
----------------
Code disassembly (best guess):
   0:	e9 ca fc ff ff       	jmpq   0xfffffccf
   5:	e8 a8 97 bc fc       	callq  0xfcbc97b2
   a:	e9 96 fc ff ff       	jmpq   0xfffffca5
   f:	e8 ce 99 bc fc       	callq  0xfcbc99e2
  14:	e9 fd fe ff ff       	jmpq   0xffffff16
  19:	66 0f 1f 84 00 00 00 	nopw   0x0(%rax,%rax,1)
  20:	00 00
  22:	55                   	push   %rbp
  23:	48 89 fd             	mov    %rdi,%rbp
  26:	e8 97 e6 92 fc       	callq  0xfc92e6c2
* 2b:	f0 ff 4d 20          	lock decl 0x20(%rbp) <-- trapping instruction
  2f:	0f 88 a7 6f 5f 02    	js     0x25f6fdc
  35:	74 06                	je     0x3d
  37:	5d                   	pop    %rbp
  38:	e9 85 e6 92 fc       	jmpq   0xfc92e6c2
  3d:	e8                   	.byte 0xe8
  3e:	80                   	.byte 0x80
  3f:	e6                   	.byte 0xe6