linux-kernel - Re: cpufreq/ondemand: unpinning an unpinned lock.

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Date:	Thu, 16 Jul 2015 10:41:50 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Dave Jones <davej@...emonkey.org.uk>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	linux-pm@...r.kernel.org
Subject: Re: cpufreq/ondemand: unpinning an unpinned lock.

On 16-07-15, 02:13, Rafael J. Wysocki wrote:
> Cc: Viresh as he's been working on governors recently.
> 
> On Wednesday, July 15, 2015 06:04:22 PM Dave Jones wrote:
> > WARNING: CPU: 1 PID: 29529 at kernel/locking/lockdep.c:3497 lock_unpin_lock+0x109/0x110()
> > unpinning an unpinned lock
> > CPU: 1 PID: 29529 Comm: kworker/1:1 Not tainted 4.2.0-rc2-think+ #3
> > Workqueue: events od_dbs_timer
> >  0000000000000009 ffff880094d5baa8 ffffffffae7f5e6f 0000000000000007
> >  ffff880094d5baf8 ffff880094d5bae8 ffffffffae07b91a 0000000000000118
> >  00000000000000e0 ffff880507bd5c58 0000000000000092 0000000000000004
> > Call Trace:
> >  [<ffffffffae7f5e6f>] dump_stack+0x4f/0x7b
> >  [<ffffffffae07b91a>] warn_slowpath_common+0x8a/0xc0
> >  [<ffffffffae07b996>] warn_slowpath_fmt+0x46/0x50
> >  [<ffffffffae0d0ec9>] lock_unpin_lock+0x109/0x110
> >  [<ffffffffae7f93cc>] __schedule+0x3ac/0xb60
> >  [<ffffffffae7f9c41>] schedule+0x41/0x90
> >  [<ffffffffae7f9ff8>] schedule_preempt_disabled+0x18/0x30
> >  [<ffffffffae7fbcef>] mutex_lock_nested+0x16f/0x3e0
> >  [<ffffffffae69207f>] ? gov_queue_work+0x2f/0xf0
> >  [<ffffffffae690ec7>] ? od_check_cpu+0x57/0xd0
> >  [<ffffffffae69207f>] ? gov_queue_work+0x2f/0xf0
> >  [<ffffffffae69207f>] gov_queue_work+0x2f/0xf0
> >  [<ffffffffae6918dd>] od_dbs_timer+0xbd/0x150
> >  [<ffffffffae099613>] process_one_work+0x1f3/0x7a0
> >  [<ffffffffae099582>] ? process_one_work+0x162/0x7a0
> >  [<ffffffffae099cb9>] ? worker_thread+0xf9/0x470
> >  [<ffffffffae099c29>] worker_thread+0x69/0x470
> >  [<ffffffffae0ad993>] ? preempt_count_sub+0xa3/0xf0
> >  [<ffffffffae099bc0>] ? process_one_work+0x7a0/0x7a0
> >  [<ffffffffae09fddf>] kthread+0x11f/0x140
> >  [<ffffffffae09fcc0>] ? kthread_create_on_node+0x250/0x250
> >  [<ffffffffae80090f>] ret_from_fork+0x3f/0x70
> >  [<ffffffffae09fcc0>] ? kthread_create_on_node+0x250/0x250
> > ---[ end trace 86cca931caec9193 ]---

I don't know why this will happen. Just to confirm, you are getting
this over 4.2-rc(1 or 2)? And you weren't getting these on 4.1 at all?
And its always reproducible? How ?

There have been races in cpufreq core since sometime and what got
pushed in 4.2-rc1 is just half of the fix. The other half is present
here:

http://marc.info/?i=cover.1434713657.git.viresh.kumar%40linaro.org

Please try this and let us know if things work well or not.

-- 
viresh
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