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

Mel Gorman
2008-03-07T11:49:05Z

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