BUG: unable to handle kernel NULL pointer dereference at 0000000000000120
IP: set_bit arch/x86/include/asm/bitops.h:81 [inline]
IP: cpumask_set_cpu include/linux/cpumask.h:283 [inline]
IP: blk_mq_map_swqueue+0x25e/0x9c0 block/blk-mq.c:2171
PGD 91b37067 P4D 91b37067 PUD 83e44067 PMD 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
Modules linked in:
CPU: 0 PID: 16411 Comm: syz-executor.0 Not tainted 4.14.142 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff888053ac45c0 task.stack: ffff888090e28000
RIP: 0010:set_bit arch/x86/include/asm/bitops.h:81 [inline]
RIP: 0010:cpumask_set_cpu include/linux/cpumask.h:283 [inline]
RIP: 0010:blk_mq_map_swqueue+0x25e/0x9c0 block/blk-mq.c:2171
RSP: 0018:ffff888090e2fa50 EFLAGS: 00010246
RAX: 0000000000040000 RBX: 0000000000000001 RCX: ffffc90008c54000
RDX: 0000000000000000 RSI: ffffffff82ca138a RDI: ffff8880a4ab8c48
RBP: ffff888090e2fac8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: ffff888090e2f8e8 R12: 0000000000000001
R13: ffff8880a4abac80 R14: dffffc0000000000 R15: ffff8880a4bbefb0
FS:  00007f2906e59700(0000) GS:ffff8880aee00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000120 CR3: 0000000098147000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 blk_mq_queue_reinit block/blk-mq.c:2514 [inline]
 __blk_mq_update_nr_hw_queues block/blk-mq.c:2748 [inline]
 blk_mq_update_nr_hw_queues+0x21c/0x3a0 block/blk-mq.c:2758
 nbd_start_device+0x12c/0xb00 drivers/block/nbd.c:1144
 nbd_start_device_ioctl drivers/block/nbd.c:1185 [inline]
 __nbd_ioctl drivers/block/nbd.c:1256 [inline]
 nbd_ioctl+0x43d/0xae0 drivers/block/nbd.c:1296
 __blkdev_driver_ioctl block/ioctl.c:297 [inline]
 blkdev_ioctl+0x96b/0x1860 block/ioctl.c:594
 block_ioctl+0xde/0x120 fs/block_dev.c:1881
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x7ae/0x1060 fs/ioctl.c:684
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
 do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x4598e9
RSP: 002b:00007f2906e58c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f2906e58c90 RCX: 00000000004598e9
RDX: 0000000000000000 RSI: 000000000000ab03 RDI: 0000000000000005
kobject: 'loop4' (ffff8880a4a82960): kobject_uevent_env
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f2906e596d4
R13: 00000000004c31c9 R14: 00000000004d6978 R15: 0000000000000007
Code: ea 
kobject: 'loop4' (ffff8880a4a82960): fill_kobj_path: path = '/devices/virtual/block/loop4'
03 42 80 3c 32 00 0f 
kobject: 'loop5' (ffff8880a4ab3260): kobject_uevent_env
85 94 06 00 00 41 83 fc 3f 48 8b 17 0f 87 4b 04 00 00 48 89 55 c8 48 89 45 d0 e8 e6 de 92 fe 48 8b 55 c8 <f0> 48 0f ab 9a 20 01 00 00 48 8d ba 78 01 00 00 48 8b 45 d0 48 
kobject: 'loop5' (ffff8880a4ab3260): fill_kobj_path: path = '/devices/virtual/block/loop5'
RIP: set_bit arch/x86/include/asm/bitops.h:81 [inline] RSP: ffff888090e2fa50
RIP: cpumask_set_cpu include/linux/cpumask.h:283 [inline] RSP: ffff888090e2fa50
RIP: blk_mq_map_swqueue+0x25e/0x9c0 block/blk-mq.c:2171 RSP: ffff888090e2fa50
CR2: 0000000000000120
---[ end trace 42ae2a3e2e5b360e ]---