linux-kernel - Re: [tip: core/rcu] softirq: Don't try waking ksoftirqd before it has been spawned

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Date:   Wed, 14 Apr 2021 09:13:22 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "tip-bot2 for Paul E. McKenney" <tip-bot2@...utronix.de>,
        linux-tip-commits@...r.kernel.org,
        Uladzislau Rezki <urezki@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <frederic@...nel.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [tip: core/rcu] softirq: Don't try waking ksoftirqd before it
 has been spawned

On 2021-04-12 11:36:45 [-0700], Paul E. McKenney wrote:
> > Color me confused. I did not follow the discussion around this
> > completely, but wasn't it agreed on that this rcu torture muck can wait
> > until the threads are brought up?
> 
> Yes, we can cause rcutorture to wait.  But in this case, rcutorture
> is just the messenger, and making it wait would simply be ignoring
> the message.  The message is that someone could invoke any number of
> things that wait on a softirq handler's invocation during the interval
> before ksoftirqd has been spawned.

My memory on this is that the only user, that required this early
behaviour, was kprobe which was recently changed to not need it anymore.
Which makes the test as the only user that remains. Therefore I thought
that this test will be moved to later position (when ksoftirqd is up and
running) and that there is no more requirement for RCU to be completely
up that early in the boot process.

Did I miss anything?

> 
> 							Thanx, Paul

Sebastian