[LTP] memcontrol04: Fix test failure by keeping pagecache children alive

[linuxtestproject.agent@gmail.com]

Hi Pavithra,

On Mon, 27 Apr 2026, Pavithra wrote:
> memcontrol04: Fix test failure by keeping pagecache children alive

> Signed-off-by: Sachin Sant <sachinp@linux.ibm.com>, Pavithra <pavrampu@linux.ibm.com>

Each contributor must have their own Signed-off-by line:

  Signed-off-by: Sachin Sant <sachinp@linux.ibm.com>
  Signed-off-by: Pavithra <pavrampu@linux.ibm.com>

This is a bug fix; please add a Fixes: tag pointing to the commit that
introduced the broken behaviour.

> +	for (i = ARRAY_SIZE(leaf_cg); i > 0; i--) {
> +		if (!leaf_cg[i - 1])
> +			continue;
> +
> +		TST_CHECKPOINT_WAKE2(TEST_DONE,
> +				     ARRAY_SIZE(leaf_cg) - 1);
> +		tst_reap_children();
> +		break;
> +	}

ARRAY_SIZE(leaf_cg) - 1 = 3 assumes all three pagecache children were
created. If cleanup() is invoked during partial setup, TST_CHECKPOINT_WAKE2
will time out waiting for missing processes and emit a spurious TBROK.
Track the number of children actually spawned and wake only that many.

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