Re: [blk_mq_register_hctx] 29dee3c03a WARNING: CPU: 0 PID: 5 at lib/refcount.c:114 refcount_inc

[Peter Zijlstra <peterz@infradead.org>]

On Tue, Feb 28, 2017 at 12:11:17PM +0800, Fengguang Wu wrote:
> Hello,
> 
> FYI, an old blk_mq bug triggers new warnings on this commit. It's very
> reproducible and you may try the attached reproduce-* script.

> [    4.447772] kobject (ffff88001c041f10): tried to init an initialized object, something is seriously wrong.
> [    4.453395] CPU: 0 PID: 5 Comm: kworker/u2:0 Not tainted 4.10.0-01216-g29dee3c #2
> [    4.455534] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.9.3-20161025_171302-gandalf 04/01/2014
> [    4.458252] Workqueue: events_unbound async_run_entry_fn
> [    4.459708] Call Trace:
> [    4.460611]  dump_stack+0x19/0x27
> [    4.461652]  kobject_init+0xda/0xf0
> [    4.462731]  blk_mq_register_dev+0x31/0x150
> [    4.463990]  blk_register_queue+0x205/0x250
> [    4.465217]  device_add_disk+0x1ab/0x710
> [    4.466384]  sd_probe_async+0x11c/0x1e0
> [    4.467544]  async_run_entry_fn+0xbd/0x220
> [    4.468760]  process_one_work+0x4a7/0x990
> [    4.469938]  ? process_one_work+0x348/0x990
> [    4.471168]  worker_thread+0x342/0x8a0
> [    4.472300]  ? process_one_work+0x990/0x990
> [    4.473540]  kthread+0x188/0x190
> [    4.474557]  ? kthread_create_on_node+0x40/0x40
> [    4.475850]  ret_from_fork+0x31/0x40

So this was pre-existing wreckage? If so, that needs to be sorted first.
Because if the kobject stuff is broken, there's no way the refcount
stuff can begin to work.