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

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Message-ID: <20140128065316.GB27636@redhat.com>
Date:	Tue, 28 Jan 2014 01:53:16 -0500
From:	Dave Jones <davej@...hat.com>
To:	Tang Chen <tangchen@...fujitsu.com>
Cc:	David Rientjes <rientjes@...gle.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 Tue, Jan 28, 2014 at 01:17:21PM +0800, Tang Chen wrote:

 > Seeing from your earlier mail, it crashed at:
 > 
 >                  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
 > 
 > 
 > nodes=null and highest=3, they are correct. When looking into 
 > next_zones_zonelist(),
 > I cannot see why it crashed. So, can you print the zone id in the
 > for_each_zone_zonelist() loop in nr_free_zone_pages() ?
 > I want to know why it crashed. A NULL pointer ?  Which one ?

It's not so easy further in the function, because the oops scrolls off
any useful printks, there's no scrollback, and no logging..
I even tried adding some udelays to slow things down (and using boot_delay)
but that makes things just hang seemingly indefinitly.

What about that 'z' ptr though ? 0x1d08 seems like a strange address
for us to have a structure at, though I'm not too familiar with the early
boot code, so maybe we do have something down there ?

	Dave 

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