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Date: Thu, 4 Feb 2016 00:50:30 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Shilpa Bhat <shilpabhatppc@...il.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>,
Juri Lelli <juri.lelli@....com>,
Viresh Kumar <viresh.kumar@...aro.org>,
Rafael Wysocki <rjw@...ysocki.net>,
Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
Saravana Kannan <skannan@...eaurora.org>,
Peter Zijlstra <peterz@...radead.org>,
Michael Turquette <mturquette@...libre.com>,
Steve Muckle <steve.muckle@...aro.org>,
Vincent Guittot <vincent.guittot@...aro.org>,
Morten Rasmussen <morten.rasmussen@....com>,
dietmar.eggemann@....com,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups
On Thu, Feb 4, 2016 at 12:31 AM, Shilpa Bhat <shilpabhatppc@...il.com> wrote:
> Hi,
>
> On 02/03/2016 10:50 PM, Rafael J. Wysocki wrote:
>> On Wed, Feb 3, 2016 at 6:20 PM, Juri Lelli <juri.lelli@....com> wrote:
>>> On 03/02/16 21:40, Viresh Kumar wrote:
>>>> On 03-02-16, 15:54, Juri Lelli wrote:
>>>>> Ouch, I've just got this executing -f basic on Juno. :(
>>>>> It happens with the hotplug_1_by_1 test.
>>>>>
>>>
>>> [...]
>>>
>>>>
>>>> Urg..
>>>>
>>>> I failed to understand it for now though. Please test only the first 4
>>>> patches and leave the bottom three. AFAICT, this is caused by the 6th
>>>> patch.
>>>>
>>>> The first 4 are important for 4.5 and must be tested soonish.
>>>>
>>>
>>> First 4 look ok from a testing viewpoint.
>>
>> Good, thanks for the confirmation!
>>
>> I'm going to apply them and they will go to Linus next week.
>>
>> Thanks,
>> Rafael
>
> Sorry for the delayed report. But I see the below backtrace on Power8 box. It
> has 4 chips with 128 cpus.
Thanks for the report.
> I see the below trace with the first four patches on running tests
> from Viresh's testcase.
> './runme.sh -f basic'
> hit this trace at 'shuffle_governors_for_all_cpus' test.
>
> [ 906.762045] ======================================================
> [ 906.762114] [ INFO: possible circular locking dependency detected ]
> [ 906.762172] 4.5.0-rc2-sgb+ #96 Not tainted
> [ 906.762207] -------------------------------------------------------
> [ 906.762263] runme.sh/2840 is trying to acquire lock:
> [ 906.762309] (s_active#91){++++.+}, at: [<c000000000407db8>]
> kernfs_remove+0x48/0x70
> [ 906.762419]
> but task is already holding lock:
> [ 906.762476] (od_dbs_cdata.mutex){+.+.+.}, at: [<c000000000ad7594>]
> cpufreq_governor_dbs+0x64/0x7e0
> [ 906.762592]
> which lock already depends on the new lock.
>
> [ 906.762659]
> the existing dependency chain (in reverse order) is:
> [ 906.762727]
> -> #2 (od_dbs_cdata.mutex){+.+.+.}:
> [ 906.762807] [<c000000000d485b0>] mutex_lock_nested+0x90/0x590
> [ 906.762877] [<c000000000ad57f8>] update_sampling_rate+0x88/0x1c0
> [ 906.762946] [<c000000000ad5990>] store_sampling_rate+0x60/0xa0
> [ 906.763013] [<c000000000ad6af0>] governor_store+0x80/0xc0
> [ 906.763070] [<c00000000040a8a4>] sysfs_kf_write+0x94/0xc0
> [ 906.763128] [<c0000000004094a8>] kernfs_fop_write+0x188/0x1f0
> [ 906.763196] [<c000000000347b8c>] __vfs_write+0x6c/0x180
> [ 906.763254] [<c0000000003490a0>] vfs_write+0xc0/0x200
> [ 906.763311] [<c00000000034a3cc>] SyS_write+0x6c/0x110
> [ 906.763369] [<c00000000000926c>] system_call+0x38/0xd0
> [ 906.763427]
> -> #1 (&dbs_data->mutex){+.+...}:
> [ 906.763495] [<c000000000d485b0>] mutex_lock_nested+0x90/0x590
> [ 906.763563] [<c000000000ad6ac0>] governor_store+0x50/0xc0
> [ 906.763620] [<c00000000040a8a4>] sysfs_kf_write+0x94/0xc0
> [ 906.763677] [<c0000000004094a8>] kernfs_fop_write+0x188/0x1f0
> [ 906.763745] [<c000000000347b8c>] __vfs_write+0x6c/0x180
> [ 906.763801] [<c0000000003490a0>] vfs_write+0xc0/0x200
> [ 906.763859] [<c00000000034a3cc>] SyS_write+0x6c/0x110
> [ 906.763916] [<c00000000000926c>] system_call+0x38/0xd0
> [ 906.763973]
> -> #0 (s_active#91){++++.+}:
> [ 906.764052] [<c00000000015f318>] lock_acquire+0xd8/0x1a0
> [ 906.764111] [<c0000000004065f4>] __kernfs_remove+0x344/0x410
> [ 906.764179] [<c000000000407db8>] kernfs_remove+0x48/0x70
> [ 906.764236] [<c00000000040b868>] sysfs_remove_dir+0x78/0xd0
> [ 906.764304] [<c0000000005eccec>] kobject_del+0x2c/0x80
> [ 906.764362] [<c0000000005ec9e8>] kobject_release+0xa8/0x250
> [ 906.764430] [<c000000000ad7c28>] cpufreq_governor_dbs+0x6f8/0x7e0
> [ 906.764497] [<c000000000ad4bdc>] od_cpufreq_governor_dbs+0x3c/0x60
> [ 906.764567] [<c000000000acf830>] __cpufreq_governor+0x1d0/0x390
> [ 906.764634] [<c000000000ad0750>] cpufreq_set_policy+0x3b0/0x450
> [ 906.764703] [<c000000000ad12cc>] store_scaling_governor+0x8c/0xf0
> [ 906.764771] [<c000000000aced34>] store+0xb4/0x110
> [ 906.764828] [<c00000000040a8a4>] sysfs_kf_write+0x94/0xc0
> [ 906.764885] [<c0000000004094a8>] kernfs_fop_write+0x188/0x1f0
> [ 906.764952] [<c000000000347b8c>] __vfs_write+0x6c/0x180
> [ 906.765048] [<c0000000003490a0>] vfs_write+0xc0/0x200
> [ 906.765160] [<c00000000034a3cc>] SyS_write+0x6c/0x110
> [ 906.765272] [<c00000000000926c>] system_call+0x38/0xd0
> [ 906.765384]
> other info that might help us debug this:
>
> [ 906.765522] Chain exists of:
> s_active#91 --> &dbs_data->mutex --> od_dbs_cdata.mutex
>
> [ 906.765768] Possible unsafe locking scenario:
>
> [ 906.765880] CPU0 CPU1
> [ 906.765969] ---- ----
> [ 906.766058] lock(od_dbs_cdata.mutex);
> [ 906.766170] lock(&dbs_data->mutex);
> [ 906.766304] lock(od_dbs_cdata.mutex);
> [ 906.766461] lock(s_active#91);
> [ 906.766572]
> *** DEADLOCK ***
This is exactly right. We've avoided one deadlock only to trip into
another one.
This happens because update_sampling_rate() acquires
od_dbs_cdata.mutex which is held around cpufreq_governor_exit() by
cpufreq_governor_dbs().
Worse yet, a deadlock can still happen without (the new)
dbs_data->mutex, just between s_active and od_dbs_cdata.mutex if
update_sampling_rate() runs in parallel with
cpufreq_governor_dbs()->cpufreq_governor_exit() and the latter wins
the race.
It looks like we need to drop the governor mutex before putting the
kobject in cpufreq_governor_exit().
Thanks,
Rafael
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