selftests/mm: confirm VA exhaustion without reliance on correctness of mmap()

Currently, VA exhaustion is being checked by passing a hint to mmap() and
expecting it to fail.

While populating the lower VA space, mmap() fails because we have 
exhausted the space.

Then, in validate_lower_address_hint(), because mmap() fails, we
confirm that we have indeed exhausted the space.  There is a circular
logic involved here.

Assume that there is a bug in mmap(), also assume that it exists
independent of whether you pass a hint address or not; that for some
reason it is not able to find a 1GB chunk.  My idea is to assert the
exhaustion against some other method.

This patch makes a stricter test by successful
write() calls from /proc/self/maps to a dump file, confirming that a free
chunk is indeed not available.

[[email protected]: replace SZ_1GB with MAP_CHUNK_SIZE, tidy-up]
  Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Dev Jain <[email protected]>
Cc: Anshuman Khandual <[email protected]>
Cc: Shuah Khan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions