[PATCH v2 0/2] maple_tree: Fix mas_prev() state regression.

[Liam R. Howlett]

Pedro Falcato retported an mprotect regression [1] which was bisected back
to the iterator changes for maple tree.  Root cause analysis showed the
mas_prev() running off the end of the VMA space (previous from 0)
followed by mas_find(), would skip the first value.

This patch set introduces maple state underflow/overflow so the sequence
of calls on the maple state will return what the user expects.

Users who encounter this bug may see mprotect(), userfaultfd_register(),
and mlock() fail on VMAs mapped with address 0.

[1]  https://bugs.archlinux.org/task/79656

Liam R. Howlett (2):
  maple_tree: Add mas_is_active() to detect in-tree walks
  maple_tree: Add MAS_UNDERFLOW and MAS_OVERFLOW states

 include/linux/maple_tree.h |  11 ++
 lib/maple_tree.c           | 221 +++++++++++++++++++++++++++----------
 lib/test_maple_tree.c      |  87 ++++++++++++---
 3 files changed, 246 insertions(+), 73 deletions(-)

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2.40.1