linux-kernel - Re: [PATCH 20/37] softirq: Introduce disabled softirq vectors bits

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Date:   Fri, 1 Mar 2019 12:29:15 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "David S . Miller" <davem@...emloft.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Pavan Kondeti <pkondeti@...eaurora.org>,
        Ingo Molnar <mingo@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: Re: [PATCH 20/37] softirq: Introduce disabled softirq vectors bits

On 2019-02-28 18:12:25 [+0100], Frederic Weisbecker wrote:
> --- a/include/linux/interrupt.h
> +++ b/include/linux/interrupt.h
> @@ -474,17 +474,62 @@ enum
…
> +static inline unsigned int local_softirq_pending(void)
> +{
> +	return local_softirq_data() & SOFTIRQ_PENDING_MASK;
> +}
…

I'm still digesting but…

> +static inline void softirq_enabled_set(unsigned int enabled)
> +{
> +	unsigned int data;
> +
> +	data = enabled << SOFTIRQ_ENABLED_SHIFT;
> +	data |= local_softirq_pending();

if an interrupt occurs at this point and invokes
	raise_softirq_irqof() => softirq_pending_set_mask()
	
then we lose the pending bits, correct? This may be invoked from
	local_bh_enable() => local_bh_enable_ip_mask() =>
	local_bh_enable_common() => softirq_enabled_set()

and as far as I can, interrupts are only disabled in the tracing case.

> +	__this_cpu_write(local_softirq_data_ref, data);
> +}

Sebastian