Re: [PATCH] PM / OPP: list_del_rcu should be used in function _remove_list_dev

[Viresh Kumar <viresh.kumar@linaro.org>]

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@spreadtrum.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@vger.kernel.org>     # 4.4
> > Signed-off-by: Vincent Wang <vincent.wang@spreadtrum.com>
> > Signed-off-by: Chunyan Zhang <chunyan.zhang@spreadtrum.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 ?

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.

-- 
viresh