INFO: task kworker/u8:0:12 blocked for more than 144 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:kworker/u8:0    state:D stack:22568 pid:12    tgid:12    ppid:2      task_flags:0x4208160 flags:0x00080000
Workqueue: netns cleanup_net
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5583 [inline]
 __schedule+0x17dd/0x5820 kernel/sched/core.c:7382
 __schedule_loop kernel/sched/core.c:7459 [inline]
 schedule+0x164/0x2b0 kernel/sched/core.c:7474
 schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7531
 rwsem_down_write_slowpath+0x874/0x10d0 kernel/locking/rwsem.c:1215
 __down_write_common kernel/locking/rwsem.c:1347 [inline]
 __down_write kernel/locking/rwsem.c:1356 [inline]
 down_write+0x1b7/0x200 kernel/locking/rwsem.c:1632
 rdma_dev_exit_net+0x8b/0x430 drivers/infiniband/core/device.c:1156
 ops_exit_list net/core/net_namespace.c:200 [inline]
 ops_undo_list+0x451/0x8f0 net/core/net_namespace.c:253
 cleanup_net+0x572/0x810 net/core/net_namespace.c:706
 process_one_work kernel/workqueue.c:3495 [inline]
 process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3578
 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3659
 kthread+0x38b/0x480 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>

Showing all locks held in the system:
locks held by kthreadd/2: 1, last CPU#1:
 #0: ffffffff8feaa030 (remove_cache_srcu){.+.+}-{0:0}, at: srcu_lock_acquire include/linux/srcu.h:213 [inline]
 #0: ffffffff8feaa030 (remove_cache_srcu){.+.+}-{0:0}, at: srcu_read_lock+0x27/0x60 include/linux/srcu.h:320
locks held by kworker/u8:0/12: 4, on CPU#0:
 #0: ffff88801d2de148 ((wq_completion)netns){+.+.}-{0:0}, at: rcu_lock_acquire include/linux/rcupdate.h:309 [inline]
 #0: ffff88801d2de148 ((wq_completion)netns){+.+.}-{0:0}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline]
 #0: ffff88801d2de148 ((wq_completion)netns){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3460 [inline]
 #0: ffff88801d2de148 ((wq_completion)netns){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630 kernel/workqueue.c:3578
 #1: ffffc90000117c40 (net_cleanup_work){+.+.}-{0:0}, at: rcu_lock_acquire include/linux/rcupdate.h:309 [inline]
 #1: ffffc90000117c40 (net_cleanup_work){+.+.}-{0:0}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline]
 #1: ffffc90000117c40 (net_cleanup_work){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3460 [inline]
 #1: ffffc90000117c40 (net_cleanup_work){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630 kernel/workqueue.c:3578
 #2: ffffffff91268248 (pernet_ops_rwsem){++++}-{4:4}, at: cleanup_net+0xf5/0x810 net/core/net_namespace.c:677
 #3: ffffffff90fcc608 (rdma_nets_rwsem){++++}-{4:4}, at: rdma_dev_exit_net+0x8b/0x430 drivers/infiniband/core/device.c:1156
locks held by kworker/u8:1/13: 3, last CPU#0:
 #0: ffff88801c0ac148 ((wq_completion)events_unbound){+.+.}-{0:0}, at: rcu_lock_acquire include/linux/rcupdate.h:309 [inline]
 #0: ffff88801c0ac148 ((wq_completion)events_unbound){+.+.}-{0:0}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline]
 #0: ffff88801c0ac148 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3460 [inline]
 #0: ffff88801c0ac148 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630 kernel/workqueue.c:3578