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

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Message-ID: <20160105091444.GZ6357@twins.programming.kicks-ass.net>
Date:	Tue, 5 Jan 2016 10:14:44 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Byungchul Park <byungchul.park@....com>
Cc:	stable@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [STABLE] kernel oops which can be fixed by peterz's patches

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.

> 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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