------- Comment From geral...@de.ibm.com 2017-09-20 08:56 EDT-------
It doesn't look like "brk_near_huge" is hanging, but rather the next test 
"task-size-overrun". The Assertion failure originates from "brk_near_huge", but 
that is probably unrelated to the hanging "task-size-overrun".

Also, "task-size-overrun" may only appear to be hanging, IIRC this test
will try to figure out the TASK_SIZE by successively allocating 4K pages
as long as possible. We already had an issue there on s390, with our
dynamic pagetable upgrade feature, which was fixed by the following
libhugetlbfs commit:

commit a06eeed7e005af579169f3020d3980198eb3ba30
Author: Gerald Schaefer <gerald.schae...@de.ibm.com>
Date:   Thu Mar 7 15:41:58 2013 +0100

task-size-overrun: fix problem with dynamic pagetable upgrade on s390x
The strategy to find out TASK_SIZE won't work on s390x anymore, starting
with kernel 3.9. We will dynamically increase the pagetable levels on
s390x on access beyond TASK_SIZE, effectively increasing TASK_SIZE from
2^42 to 2^53, but /proc/self/maps won't reflect this.
With the current strategy that means that find_task_size() would loop
for a very long time, from 2^42 to 2^53. To fix this, increase addr
in the loop for s390x as soon as we exceed the 2^42 limit.
Signed-off-by: Gerald Schaefer <gerald.schae...@de.ibm.com>
Signed-off-by: Eric B Munson <emun...@mgebm.net>

Since we only recently added 5-level pagetable support, I guess this fix
no longer helps, as we will now loop from 2^53 to 2^64. I'll look into
this, we probably need to update "task-size-overrun" again to reflect
the 5-level pagetable update.

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https://bugs.launchpad.net/bugs/1718107

Title:
  brk_near_huge test will hang on IBM s390x zKVM / zVM

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