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

On Tue, Feb 28, 2017 at 04:35:08PM +0800, Fengguang Wu wrote:

On Tue, Feb 28, 2017 at 09:17:11AM +0100, Peter Zijlstra wrote:

quoted

On Tue, Feb 28, 2017 at 12:11:17PM +0800, Fengguang Wu wrote:

quoted

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.

quoted

[    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.

Yeah it's old bug that should have existed for quite some time.
It's not quite related to the refcount work, just hoping the new
warning might serve as new clues to help debugging the blk_mq bug.

Thanks,
Fengguang

Ming Lei posted a series to fix this here [1]. I haven't gotten around
to testing it, but it'd be great if you could try it, too.

http://marc.info/?l=linux-block&m=148775846217069&w=2