mas_empty_area_rev() was not correctly validating the start of a gap
against the lower limit. This could lead to the range starting lower
than the requested minimum.
Fix the issue by better validating a gap once one is found.
This commit also adds tests to the maple tree test suite for this issue
and tests the mas_empty_area() function for similar bound checking.
Cc: stable@xxxxxxxxxxxxxxx
BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=216911
Reported-by: amanieu@xxxxxxxxx
Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Link: https://lore.kernel.org/linux-mm/0b9f5425-08d4-8013-aa4c-e620c3b10bb2@xxxxxxxxxxxxx/
Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>