linux-kernel - Re: mmotm 2015-01-22-15-04: qemu failure due to 'mm: memcontrol: remove unnecessary soft limit tree node test'

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Date:	Fri, 23 Jan 2015 11:03:35 -0500
From:	Johannes Weiner <hannes@...xchg.org>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	akpm@...ux-foundation.org, mm-commits@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org, linux-next@...r.kernel.org,
	sfr@...b.auug.org.au, mhocko@...e.cz, cl@...ux.com
Subject: Re: mmotm 2015-01-22-15-04: qemu failure due to 'mm: memcontrol:
 remove unnecessary soft limit tree node test'

On Fri, Jan 23, 2015 at 07:46:43AM -0800, Guenter Roeck wrote:
> I added some debugging. First, the problem is only seen with SMP disabled.
> Second, there is only one online node.
> 
> Without your patch:
> 
> Node 0 online 1 high 1 memory 1 cpu 0 normal 1 tmp 0 rtpn c00000003d240600
> Node 1 online 0 high 0 memory 0 cpu 0 normal 0 tmp -1 rtpn c00000003d240640
> Node 2 online 0 high 0 memory 0 cpu 0 normal 0 tmp -1 rtpn c00000003d240680
> 
> [ and so on up to node 255 ]
> 
> With your patch:
> 
> Node 0 online 1 high 1 memory 1 cpu 0 normal 1 rtpn c00000003d240600
> Unable to handle kernel paging request for data at address 0x0000af50
> Faulting instruction address: 0xc000000000895a3c
> Oops: Kernel access of bad area, sig: 11 [#1]
> 
> The log message is after the call to kzalloc_node.
> 
> So it doesn't look like the fallback is working, at least not with ppc64
> in non-SMP mode.

Yep, and Christoph confirmed that it's not meant to work like that.
The patch is flawed.

Thanks for testing and sorry for breaking your setup.
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