Add a comment to explain the purpose of the rcu_momentary_eqs() call
from multi_cpu_stop(), which is to suppress false-positive RCU CPU
stall warnings.

Reported-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/87wmeuanti.ffs@tglx/
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
Cc: Frederic Weisbecker <frederic@kernel.org>
---
 stop_machine.c |    1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index 8896d844d738f..5d2d0562115b3 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -250,6 +250,7 @@ static int multi_cpu_stop(void *data)
 			 * be detected and reported on their side.
 			 */
 			touch_nmi_watchdog();
+			/* Also suppress RCU CPU stall warnings. */
 			rcu_momentary_eqs();
 		}
 	} while (curstate != MULTI_STOP_EXIT);