On RT a task which has soft interrupts disabled can block on a lock and
schedule out to idle while soft interrupts are pending. This triggers the
warning in the NOHZ idle code which complains about going idle with pending
soft interrupts. But as the task is blocked soft interrupt processing is
temporarily blocked as well which means that such a warning is a false
positive.

To prevent that check the per CPU state which indicates that a scheduled
out task has soft interrupts disabled.
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Tested-by: NSebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: NPaul E. McKenney <paulmck@kernel.org>
Reviewed-by: NFrederic Weisbecker <frederic@kernel.org>
Acked-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210309085727.527563866@linutronix.de