mm: avoid passing 0 to __ffs()

23baf831a32c ("mm, treewide: redefine MAX_ORDER sanely") results in
various boot failures (hang) on arm targets Debug messages reveal the
reason.

########### MAX_ORDER=10 start=0 __ffs(start)=-1 min()=10 min_t=-1
                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

If start==0, __ffs(start) returns 0xfffffff or (as int) -1, which min_t()
interprets as such, while min() apparently uses the returned unsigned long
value. Obviously a negative order isn't received well by the rest of the
code.

[[email protected]: fix comment, per Mike]
  Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Fixes: 23baf831a32c ("mm, treewide: redefine MAX_ORDER sanely")
Signed-off-by: "Kirill A. Shutemov" <[email protected]>
Reported-by: Guenter Roeck <[email protected]>
  Link: https://lkml.kernel.org/r/[email protected]
Reviewed-by: Mike Rapoport (IBM) <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions