sched/numa: Find an alternative idle CPU if the CPU is part of an active NUMA balance

Multiple tasks can attempt to select and idle CPU but fail because
numa_migrate_on is already set and the migration fails. Instead of failing,
scan for an alternative idle CPU. select_idle_sibling is not used because
it requires IRQs to be disabled and it ignores numa_migrate_on allowing
multiple tasks to stack. This scan may still fail if there are idle
candidate CPUs due to races but if this occurs, it's best that a task
stay on an available CPU that move to a contended one.

Signed-off-by: Mel Gorman <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Cc: Vincent Guittot <[email protected]>
Cc: Juri Lelli <[email protected]>
Cc: Dietmar Eggemann <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Valentin Schneider <[email protected]>
Cc: Phil Auld <[email protected]>
Cc: Hillf Danton <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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