------------[ cut here ]------------
timer_delete_sync(&sdp->delay_work) && rcu_segcblist_n_cbs(&sdp->srcu_cblist)
WARNING: kernel/rcu/srcutree.c:706 at cleanup_srcu_struct+0x6e4/0xb30 kernel/rcu/srcutree.c:706, CPU#0: kworker/u33:4/74
Modules linked in:
CPU: 0 UID: 0 PID: 74 Comm: kworker/u33:4 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Workqueue: nbd-del nbd_dev_remove_work
RIP: 0010:cleanup_srcu_struct+0x6e4/0xb30 kernel/rcu/srcutree.c:706
Code: 00 fc ff df 48 c1 ea 03 80 3c 02 00 0f 85 f4 03 00 00 48 8b 83 e8 00 00 00 48 8d 93 80 01 00 00 48 85 c0 0f 84 a7 fc ff ff 90 <0f> 0b 90 48 8d 8b 00 02 00 00 48 b8 00 00 00 00 00 fc ff df 48 89
RSP: 0018:ffffc90000fc7b60 EFLAGS: 00010202
RAX: 0000000000000004 RBX: ffffe8fefc448f80 RCX: 0000000000000000
RDX: ffffe8fefc449100 RSI: ffffffff81f703bf RDI: ffff88801d368000
RBP: ffff88802b5bf000 R08: 0000000000000005 R09: 00000000ffffffff
R10: 0000000000000001 R11: 0000000000000000 R12: ffff88802b5ba910
R13: 0000000000000000 R14: ffffffff8e65b0b0 R15: ffff88802b5ba950
FS:  0000000000000000(0000) GS:ffff8880d5b4f000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f9301deb840 CR3: 000000003f80d000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 blk_mq_free_tag_set+0x354/0x550 block/blk-mq.c:4976
 nbd_dev_remove+0x43/0xe0 drivers/block/nbd.c:270
 process_one_work+0xac7/0x1b10 kernel/workqueue.c:3396
 process_scheduled_works kernel/workqueue.c:3479 [inline]
 worker_thread+0x5ef/0xe50 kernel/workqueue.c:3560
 kthread+0x373/0x450 kernel/kthread.c:436
 ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>