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

[Greg Kroah-Hartman]

On Mon, Dec 18, 2017 at 10:57:17AM +0100, Greg Kroah-Hartman wrote:
> On Mon, Dec 18, 2017 at 05:37:38PM +0800, Chunyan Zhang wrote:
> > From: Vincent Wang <vincent.wang@xxxxxxxxxxxxxx>
> > 
> > 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@xxxxxxxxxxxxxxx>     # 4.4
> > Signed-off-by: Vincent Wang <vincent.wang@xxxxxxxxxxxxxx>
> > Signed-off-by: Chunyan Zhang <chunyan.zhang@xxxxxxxxxxxxxx>
> > Acked-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
> > ---
> > This patch is for 4.4 stable branch only.
> > Once this patch accepted, I can cook a similar patch for 4.9 stable branch.
> 
> I need that one first, as you don't want to regress from a working 4.4
> release when moving to a 4.9 release, right?
> 
> > This fix can't be done to upstream kernel as the OPP code doesn't
> > use RCUs anymore.
> 
> What was the upstream fix that changed this?  Why is this not a problem
> in 4.14?  In Linus's tree?
> 
> I _REALLY_ do not like taking patches that are not in Linus's tree, as
> when we do that, we almost always get it wrong.  Seriously, our track
> record here is horrid.
> 
> So I need a lot of assurance that this is the correct fix, that it has
> been tested properly, and that there really is no way to take the
> upstream patches instead of your one-off patch.
> 
> Also, what commit does this fix?  When did the bug show up?  When did it
> go away?  Why not include a Fixes: line?
> 
> See, a lot more work needs to be done here, as I said previously :)
> 
> Taking patches that are not in Linus's tree is a very expensive, and
> difficult thing, for good reason.

Now dropped from my queue due to lack of response, if you want this
applied, please address the questions I have above and resend.

thanks,

greg k-h