linux-kernel - Re: [REGRESSION] funny sched_domain build failure during resume

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Message-ID: <20140514171051.GX30445@twins.programming.kicks-ass.net>
Date:	Wed, 14 May 2014 19:10:51 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Johannes Weiner <hannes@...xchg.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Juri Lelli <juri.lelli@...il.com>
Subject: Re: [REGRESSION] funny sched_domain build failure during resume

On Wed, May 14, 2014 at 01:02:38PM -0400, Tejun Heo wrote:
> On Wed, May 14, 2014 at 04:00:34PM +0200, Peter Zijlstra wrote:
> > Does something like the below help any? I noticed those things (cpudl
> > and cpupri) had [NR_CPUS] arrays, which is always 'fun'.
> > 
> > The below is a mostly no thought involved conversion of cpudl which
> > boots, I'll also do cpupri and then actually stare at the algorithms to
> > see if I didn't make any obvious fails.
> 
> Yeah, should avoid large allocation on reasonably sized machines and I
> don't think 2k CPU machines suspend regularly.  Prolly good / safe
> enough for -stable port?  

Yeah, its certainly -stable material. Esp. if this cures the immediate
problem.

> It'd be still nice to avoid allocations if
> possible during online tho given that the operation happens while mm
> is mostly crippled.

Yeah, I started looking at that but that turned out to be slightly more
difficult than I had hoped (got lost in the suspend code). Also avoiding
large order allocs is good practise regardless.

So probably the easiest way to not free/alloc the entire sched_domain
thing is just keeping it around in its entirety over suspend/resume, as
I think the promise of suspend/resume is that you return to the
status-quo.

But I'll stick it on the todo list after fixing this use-after-free
thing I've been trying to chase down.

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