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