stop_machine: Fix rcu_momentary_eqs() call in multi_cpu_stop()

The multi_cpu_stop() contains a loop that can initially be executed with
interrupts enabled (in the MULTI_STOP_NONE and MULTI_STOP_PREPARE states).
Interrupts are guaranteed to be once the MULTI_STOP_DISABLE_IRQ state
is reached.  Unfortunately, the rcu_momentary_eqs() function that is
currently invoked on each pass through this loop requires that interrupts
be disabled.

This commit therefore moves this call to rcu_momentary_eqs() to the body
of the "else if (curstate > MULTI_STOP_PREPARE)" portion of the loop, thus
guaranteeing that interrupts will be disabled on each call, as required.

Kudos to 朱恺乾 (Kaiqian) for noting that this had not made it to mainline.

[ paulmck: Update from rcu_momentary_dyntick_idle() to rcu_momentary_eqs(). ]

Link: https://lore.kernel.org/all/1712649736-27058-1-git-send-email-quic_mojha@quicinc.com/



Signed-off-by: Mukesh Ojha <quic_mojha@quicinc.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>