linux-kernel - Re: [BUG] 2.6.25-rc4 hang/softlockups after freeing hugepages

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Date:	Fri, 7 Mar 2008 11:48:49 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	Lee Schermerhorn <Lee.Schermerhorn@...com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>, Adam Litke <agl@...ibm.com>,
	Nishanth Aravamudan <nacc@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Eric Whitney <eric.whitney@...com>
Subject: Re: [BUG] 2.6.25-rc4 hang/softlockups after freeing hugepages

On (06/03/08 12:23), Lee Schermerhorn didst pronounce:
> Test platform:  HP Proliant DL585 server - 4 socket, dual core AMD with
> 32GB memory.
> 
> I first saw this on 25-rc2-mm1 with Mel's zonelist patches, while
> investigating the interaction of hugepages and cpusets.  Thinking that
> it might be caused by the zonelist patches, I went back to 25-rc2-mm1
> w/o the patches and saw the same thing.  It sometimes takes a while for
> the softlockups to start appearing, and I wanted to find a fairly
> minimal duplicator.  Meanwhile 25-rc3 and rc4 have come out, so I tried
> the latest upstream kernel and see the same thing.
> 
> To duplicate the problem, I need only:
> 
> + log into the platform as root in one window and:
> 
> 	echo N >/proc/sys/vm/nr_hugepages
> 	echo 0 >proc/sys/vm/nr_hugepages
> 

Uncool, I am going to try and find a machine to reproduce this one but
in case I have no luck, can you try setting the following in your
.config which may rattle out something please?

CONFIG_DEBUG_SPINLOCK=y
CONFIG_DEBUG_MUTEXES=y
CONFIG_DEBUG_LOCK_ALLOC=y
CONFIG_PROVE_LOCKING=y
CONFIG_DEBUG_SPINLOCK_SLEEP=y
CONFIG_DEBUG_VM=y

and as you have DEBUG_INFO, can you say what line is ffffffff8027b693 ?

> In my case, N=64.  If I look, before echoing 0, I see 16 hugepages
> allocated on each of the 4 nodes, as expected.
> 
> + then in another window, log in again.  
> 
> Sometimes it will hang during the 2nd login and I'll never see a shell
> prompt. 

My initial guess was that is is something to do with page_table_lock but as
you didn't get to fault in huge pages, it doesn't make much sense.

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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