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From:   Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To:     linux-kernel@vger.kernel.org
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Christoph Hellwig <hch@infradead.org>,
        Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH v3] smp: Wake ksoftirqd on PREEMPT_RT instead
 do_softirq().
Message-ID: <YjQ19nUE010AOboS@linutronix.de>
References: <YgKgL6aPj8aBES6G@linutronix.de>
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On 2022-02-08 17:54:08 [+0100], To linux-kernel@vger.kernel.org wrote:
> --- a/kernel/smp.c
> +++ b/kernel/smp.c
> @@ -691,10 +691,25 @@ void flush_smp_call_function_from_idle(v
>  	cfd_seq_store(this_cpu_ptr(&cfd_seq_local)->idle, CFD_SEQ_NOCPU,
>  		      smp_processor_id(), CFD_SEQ_IDLE);
>  	local_irq_save(flags);
> -	flush_smp_call_function_queue(true);
> -	if (local_softirq_pending())
> -		do_softirq();

One thing I noticed while looking for a possible PI-boost from idle/
sched_core_balance(): Interrupts are disabled by the caller right before
calling this function or that local_irq_save() here. That do_softirq()
below, may enable interrupts while invoking softirqs. Both caller don't
have a lock acquired so it should be okay.

Sebastian