linux-kernel - Re: [PATCH] numa, mem-hotplug: Fix stack overflow in numa when seting kernel nodes to unhotpluggable.

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Message-ID: <20140123223136.GA18468@redhat.com>
Date:	Thu, 23 Jan 2014 17:31:36 -0500
From:	Dave Jones <davej@...hat.com>
To:	David Rientjes <rientjes@...gle.com>,
	Tang Chen <tangchen@...fujitsu.com>, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, akpm@...ux-foundation.org,
	zhangyanfei@...fujitsu.com, guz.fnst@...fujitsu.com,
	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] numa, mem-hotplug: Fix stack overflow in numa when
 seting kernel nodes to unhotpluggable.

On Thu, Jan 23, 2014 at 01:58:24AM -0500, Dave Jones wrote:

 > 128 bytes is a pretty small amount of stack though, so I'm just as confused
 > as to what the actual bug here is.
 > 
 > After trying the proposed fix, I got another oops in the early init code..
 > 
 > <trace>
 > nr_free_zone_pages
 > nr_free_pagecache_pages
 > build_all_zonelists
 > start_kernel
 > <rip> ffffffffbc164b1e next_zones_zonelist
 > <rsp> ffffffffbcc01f00

Ok, this is crashing here in next_zones_zonelist...

                while (zonelist_zone_idx(z) > highest_zoneidx)
  de:   3b 77 08                cmp    0x8(%rdi),%esi


I stuck this at the top of the function..

printk(KERN_ERR "z:%p nodes:%p highest:%d\n", z, nodes, highest_zoneidx);

and got

z: 1d08   nodes: (null)  highest:3


Some build tests show..

MAXSMP ( NODESHIFT=10 ) : Bug
NRCPUS=4 & NODESHIFT=10 : Bug
NRCPUS=4 & NODESHIFT=1 : no bug


The middle config test was accidental, I hadn't realised disabling MAXSMP
wouldn't reset NODESHIFT to something sane.

I'll start bisecting, as MAXSMP worked fine until a few days ago.

	Dave

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