mmap(2) allows for a destination address to be specified without MAP_FIXED and in this situation it's a hint to get_unmapped_area(). This address need not be page aligned because get_unmapped_area() will align the hint. In the case of mremap(2) with MREMAP_DONTUNMAP it shares a code path with MREMAP_FIXED in mremap_to(), which means this function can be called in 3 different scenarios: MREMAP_FIXED only, MREMAP_DONTUNMAP only, or MREMAP_FIXED | MREMAP_DONTUNMAP. In the second case when only MREMAP_DONTUNMAP is specified we don't need to do alignment or size checks on newaddr because they will be passed to get_unmapped_area() and dealt with appropriately. This patch corrects that behavior to match what non-MREMAP_DONTUNMAP mremap(2) and mmap(2) do. This odd behavioral difference was reported by Marco Vanotti. Additionally, I've included a self test to validate this behavior. Brian Geffon (2): mremap: Fix new_addr being used as a hint with MREMAP_DONTUNMAP selftests: mm: Add a new MREMAP_DONTUNMAP self test mm/mremap.c | 26 ++++++++---- tools/testing/selftests/mm/mremap_dontunmap.c | 41 ++++++++++++++++++- 2 files changed, 59 insertions(+), 8 deletions(-) -- 2.47.0.338.g60cca15819-goog
