maple_tree: fix status setup on restore to active

maple_tree: fix status setup on restore to active

During the initial call with a maple state, an error status may be set
before a valid node is populated into the maple state node.  Subsequent
calls with the maple state may restore the state into an active state with
no node set.  This was masked by the mas_walk() always resetting the
status to ma_start and result in an extra walk in this rare scenario.

Don't restore the state to active unless there is a value in the structs
node.  This also allows mas_walk() to be fixed to use the active state
without exposing an issue.

User visible results are marginal performance improvements when an active
state can be restored and used instead of rewalking the tree.

Stable is not Cc'ed because the existing code is stable and the
performance gains are not worth the risk.

Link: https://lore.kernel.org/all/20250611011253.19515-1-richard.weiyang@gmail.com/
Link: https://lore.kernel.org/all/20250407231354.11771-1-richard.weiyang@gmail.com/
Link: https://lore.kernel.org/all/202506191556.6bfc7b93-lkp@intel.com/
Link: https://lkml.kernel.org/r/20250624154823.52221-1-Liam.Howlett@oracle.com
Fixes: a8091f039c1e ("maple_tree: add MAS_UNDERFLOW and MAS_OVERFLOW states")
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Reported-by: Wei Yang <richard.weiyang@gmail.com>
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202506191556.6bfc7b93-lkp@intel.com
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>