linux-kernel - Re: [PATCH v4] sched/numa, mm: do not try to migrate memory to memoryless nodes

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Date: Tue, 20 Feb 2024 12:20:08 +0900
From: Byungchul Park <byungchul@...com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: "Huang, Ying" <ying.huang@...el.com>, mingo@...hat.com,
	peterz@...radead.org, juri.lelli@...hat.com,
	vincent.guittot@...aro.org, dietmar.eggemann@....com,
	rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
	bristot@...hat.com, vschneid@...hat.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	kernel_team@...ynix.com
Subject: Re: [PATCH v4] sched/numa, mm: do not try to migrate memory to
 memoryless nodes

On Mon, Feb 19, 2024 at 07:05:20PM -0800, Andrew Morton wrote:
> On Tue, 20 Feb 2024 10:53:43 +0900 Byungchul Park <byungchul@...com> wrote:
> 
> > > > IIUC, you will use patch as fix to the issue in
> > > > 
> > > > https://lore.kernel.org/lkml/20240216111502.79759-1-byungchul@sk.com/
> > > > 
> > > > If so, we need the Fixes: tag to make it land in -stable properly.
> > > 
> > > Yes, this changelog is missing rather a lot of important information.
> > 
> > This is not the root cause fix any more but just optimization.
> 
> It would have been helpful to have told us this in the changelog :(

Sorry for that and making you guys confused.

> > That's
> > why I didn't add Fixes: tag and cc stable@...r.kernel.org in here.
> > 
> > Instead, I added Fixes: tag and cc'ed stable@...r.kernel.org in the real
> > fix patch. check the following link please:
> > 
> > https://lore.kernel.org/lkml/20240216111502.79759-1-byungchul@sk.com/
> 
> But doesn't this patch "sched/numa, mm: do not try to migrate memory to
> memoryless nodes" also fix the bug?  Do we truly need both?

Yes. The oops is gone with "sched/numa, mm: do not try to migrate memory
to memoryless nodes". However, as you know, wrongly manipulating array
index is very dangerous - what hackers are looking for. Even with security
in mind, both are necessary. Plus, no one gurantees the problematic code
is gone through with a numa node that has no managed zones in the future.

	Byungchul