Re: [STABLE] kernel oops which can be fixed by peterz's patches

[Byungchul Park <byungchul.park@lge.com>]

On Tue, Jan 05, 2016 at 10:14:44AM +0100, Peter Zijlstra wrote:
> On Tue, Jan 05, 2016 at 05:52:11PM +0900, Byungchul Park wrote:
> > 
> > Upstream commits to be applied
> > ==============================
> > 
> > e3fca9e: sched: Replace post_schedule with a balance callback list
> > 4c9a4bc: sched: Allow balance callbacks for check_class_changed()
> > 8046d68: sched,rt: Remove return value from pull_rt_task()
> > fd7a4be: sched, rt: Convert switched_{from, to}_rt() / prio_changed_rt() to balance callbacks
> > 0ea60c2: sched,dl: Remove return value from pull_dl_task()
> > 9916e21: sched, dl: Convert switched_{from, to}_dl() / prio_changed_dl() to balance callbacks
> > 
> > The reason why these should be applied
> > ======================================
> > 
> > Our products developed using 3.16 kernel, faced a kernel oops which can
> > be fixed with above upstreamed patches. The oops is caused by "Unable
> > to handle kernel NULL pointer dereference at virtual address 000000xx"
> > in the call path,
> > 
> > __sched_setscheduler()
> > 	check_class_changed()
> > 		switched_to_fair()
> > 			check_preempt_curr()
> > 				check_preempt_wakeup()
> > 					find_matching_se()
> > 						is_same_group()
> > 
> > by "if (se->cfs_rq == pse->cfs_rq) // se, pse == NULL" condition.
> 
> So the reason I didn't mark them for stable is that they were non
> trivial, however they've been in for a while now and nothing broke, so I
> suppose backporting them isn't a problem.

Do you think the backporting can have some potential problems? I
checked if it worked well on my machine. Do you think it need more
tests to verify its stability?

> 
> > How to apply it
> > ===============
> > 
> > For stable 4.2.8+:
> > 	N/A (already applied)
> > 
> > For longterm 4.1.15:
> > 	Cherry-picking the upsteam commits works with a trivial conflict.
> > 
> > For longterm 3.18.25:
> > 	Refer to the backported patches in this thread.
> > 
> > For longterm 3.14.58:
> > 	Refer to the backported patches in this thread. And applying
> > 	additional "6c3b4d4: sched: Clean up idle task SMP logic" commit
> > 	makes backporting the upstream commits much simpler. So my
> > 	backporting patches include the patch.
> > 
> > For longterm 2.6.32.69 ~ 3.12.51: Need to be backported. (I didn't)
> 
> No objection as long as you've actually tested things etc..
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