linux-kernel - Re: [PATCH] PM / OPP: list_del_rcu should be used in function _remove_list

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Date:   Mon, 18 Dec 2017 17:37:27 +0800
From:   Chunyan Zhang <zhang.lyra@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        Chunyan Zhang <chunyan.zhang@...eadtrum.com>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Vincent Wang <vincent.wang@...eadtrum.com>,
        Orson Zhai <orson.zhai@...eadtrum.com>
Subject: Re: [PATCH] PM / OPP: list_del_rcu should be used in function _remove_list_dev

On 18 December 2017 at 17:32, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
> On Mon, Dec 18, 2017 at 02:41:39PM +0530, Viresh Kumar wrote:
>> On 18-12-17, 10:07, Greg Kroah-Hartman wrote:
>> > On Mon, Dec 18, 2017 at 04:32:23PM +0800, Chunyan Zhang wrote:
>> > > From: Vincent Wang <vincent.wang@...eadtrum.com>
>> > >
>> > > list_del_rcu() should be used to replace list_del() in the function
>> > > _remove_list_dev(), since the opp is a rcu protected pointer.
>> > >
>> > > For example, on an ARM big.Little platform of spreadtrum, there are
>> > > little cluster, big cluster and gpu using pm_opp. And the opp_table
>> > > of big cluster will be removed when big cluster is removed, which
>> > > is implemented in the cpufreq driver. Sometimes an issue maybe occur:
>> > >
>> > > [  237.647758] c0 Unable to handle kernel paging request at virtual address dead000000000110
>> > > [  237.647776] c0 pgd = ffffffc073e78000
>> > > [  237.647786] c0 [dead000000000110] *pgd=0000000000000000, *pud=0000000000000000
>> > > [  237.647808] c0 Internal error: Oops: 96000004 [#1] PREEMPT SMP
>> > > [  237.653535] c0 Modules linked in: sprdwl_ng(O) mtty marlin2_fm mali_kbase(O)
>> > > [  237.653569] c0 CPU: 0 PID: 38 Comm: kworker/u12:1 Tainted: G S      W  O    4.4.83+ #1
>> > > [  237.653578] c0 Hardware name: Spreadtrum SP9850KHsmt 1h10 Board (DT)
>> > > [  237.653594] c0 Workqueue: devfreq_wq devfreq_monitor
>> > > [  237.653605] c0 task: ffffffc0babd0d80 task.stack: ffffffc0badbc000
>> > > [  237.653619] c0 PC is at _find_device_opp+0x58/0xac
>> > > [  237.653629] c0 LR is at dev_pm_opp_find_freq_ceil+0x2c/0xb8
>> > >
>> > > [  237.921294] c0 Call trace:
>> > > [  237.921425] c0 [<ffffff80085362b0>] _find_device_opp+0x58/0xac
>> > > [  237.921437] c0 [<ffffff8008536560>] dev_pm_opp_find_freq_ceil+0x2c/0xb8
>> > > [  237.921452] c0 [<ffffff80088760f4>] devfreq_recommended_opp+0x54/0x7c
>> > > [  237.921494] c0 [<ffffff8000b6a96c>] kbase_wait_write_flush+0x164/0x358 [mali_kbase]
>> > > [  237.921504] c0 [<ffffff800887485c>] update_devfreq+0x8c/0xf8
>> > > [  237.921514] c0 [<ffffff80088749e4>] devfreq_monitor+0x34/0x94
>> > > [  237.921529] c0 [<ffffff80080bd75c>] process_one_work+0x154/0x458
>> > > [  237.921539] c0 [<ffffff80080be428>] worker_thread+0x134/0x4a4
>> > > [  237.921551] c0 [<ffffff80080c4bec>] kthread+0xdc/0xf0
>> > > [  237.921564] c0 [<ffffff8008085f20>] ret_from_fork+0x10/0x30
>> > >
>> > > Cc: stable <stable@...r.kernel.org>     # 4.4
>> > > Signed-off-by: Vincent Wang <vincent.wang@...eadtrum.com>
>> > > Signed-off-by: Chunyan Zhang <chunyan.zhang@...eadtrum.com>
>> > > ---
>> > >
>> > > This patch is only for 4.4 stable branch.
>> > > Once this patch accepted, I can cook a similar patch for 4.9 stable branch.
>> >
>> > <formletter>
>> >
>> > This is not the correct way to submit patches for inclusion in the
>> > stable kernel tree.  Please read:
>> >     https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
>> > for how to do this properly.
>>
>> Are you worried about this not being merged upstream first ? Or something else ?
>
> Yes, and yes.
>
>> This can't be done to upstream kernel as the OPP code doesn't use RCUs anymore
>> and yes, this reason should have been part of the commit message to make things
>> clear.
>
> Yes, that too.  But the most basic issue of not cc: stable@...r is also
> a problem here :(

Sorry for the trouble, I will send this again and cc stable@...r.

Thanks,
Chunyan

>
> This needs a lot of work to go anywhere...
>
> greg k-h