linux-kernel - Re: [RFC PATCH 2/3] lockdep: Merge hardirq_threaded and irq

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Message-ID: <20200323145314.v57acriqj2s6wry2@linutronix.de>
Date:   Mon, 23 Mar 2020 15:53:14 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC PATCH 2/3] lockdep: Merge hardirq_threaded and irq_config
 together

On 2020-03-23 15:02:20 [+0100], Peter Zijlstra wrote:
> On Mon, Mar 23, 2020 at 04:32:06AM +0100, Frederic Weisbecker wrote:
> > These fields describe the same state: a code block running in hardirq
> > that might be threaded under specific configurations.
> > 
> > Merge them together in the same field. Also rename the result as
> > "hardirq_threadable" as we are talking about a possible state and not
> > an actual one.
> 
> What isn't instantly obvious is that they cannot overlap. For instance
> mainline with force threaded interrupt handlers on, can't that have the
> irq_work nest inside a threaded handler ?

I remember we kept them due to the nesting. A threaded-interrupt can be
interrupted by irq_work/hrtimer/posix-timer. 
So in a threaded interrupt it is okay to use a sleeping lock. It is not
okay with irq_work on-top - unless it is the non-atomic one.

> I *think* it just about works out, but it definitely wants a little more
> than this.

Sebastian