Re: s390 hugetlb oops with libhugetlbfs test-suite

[Nishanth Aravamudan <nacc@us.ibm.com>]

On 25.07.2008 [14:10:35 -0700], Nishanth Aravamudan wrote:
> Hi Gerald,
> 
> Having noticed that the hugetlbfs code recently got an update to work
> on s390, I decided to port the libhugetlbfs test-suite to work on
> s390. The current development snapshot is available at
> http://libhugetlbfs.ozlabs.org/snapshots/libhugetlbfs-dev-20080724.tar.gz.
> You will need a patch [1] to build on s390, but it should roughly work
> otherwise.  The specific testcase that causes the oops is counters.
> The bit set in the flags is PG_Reserved, I think.

After enabling some debugging options, I got a slightly more precise
stack trace. The last one I posted was for the 32-bit counters test and
this one is for the 64-bit one, but appears to be the same problem
(PG_reserved still being set).

Bad page state in process 'counters'
page:000003e040000000 flags:0x0000000000000400 mapping:0000000000000000 mapcount:0 count:0
Trying to fix it up, but a reboot is needed
Backtrace:
CPU: 1 Tainted: G        W 2.6.26-autokern1 #1
Process counters (pid: 5365, task: 000000003855ab50, ksp: 000000002667bbc0)
0000000000000047 000000002667b7d0 0000000000000002 0000000000000000 
       000000002667b870 000000002667b7e8 000000002667b7e8 0000000000016f22 
       0000000000000000 0000000000000000 000002000000000a 000000000000000a 
       0000000000000000 000000002667b7d0 000000002667b7d0 000000002667b848 
       000000000025cb28 0000000000016f22 000000002667b7d0 000000002667b828 
Call Trace:
([<0000000000016e80>] show_trace+0xd8/0xe8)
 [<0000000000016f40>] show_stack+0xb0/0xc0
 [<000000000001766c>] dump_stack+0xa8/0xb8
 [<000000000007f3da>] bad_page+0x9a/0xd4
 [<00000000000802dc>] free_hot_cold_page+0xa0/0x1f8
 [<00000000000804f6>] free_hot_page+0x22/0x30
 [<000000000008503a>] put_page+0x136/0x144
 [<00000000000a0a68>] __unmap_hugepage_range+0x398/0x3dc
 [<00000000000a0b00>] unmap_hugepage_range+0x54/0x7c
 [<000000000008d6f2>] unmap_vmas+0x152/0xb5c
 [<000000000009284e>] exit_mmap+0x14e/0x2fc
 [<000000000003b128>] mmput+0x64/0x110
 [<000000000004030c>] exit_mm+0xf0/0x100
 [<0000000000041fd8>] do_exit+0x268/0x7f8
 [<00000000000425fe>] do_group_exit+0x96/0xc4
 [<000000000004ddbc>] get_signal_to_deliver+0x350/0x378
 [<000000000001e026>] do_signal+0xe6/0x87c
 [<0000000000024a0a>] sysc_sigpending+0xe/0x22
 [<000000008000163c>] 0x8000163c

I'm not quite sure yet how the hugetlb destructor
(free_huge_page()/update_and_free_page()) can call
free_hot_page()/free_hot_cold_page(), because the comments for both
indicate they should only be used for order-0 pages. Are we somehow
losing the fact that this is a compound page on s390?

If anyone would like a s390-compatible version of libhugetlbfs, just let
me know I can send it off-list.

Thanks,
Nish

-- 
Nishanth Aravamudan <nacc@us.ibm.com>
IBM Linux Technology Center