linux-kernel - Re: RCU use of swait

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Message-ID: <20200305081135.yg7wryd3hrqzocrm@linutronix.de>
Date:   Thu, 5 Mar 2020 09:11:35 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     josh@...htriplett.org, rostedt@...dmis.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        joel@...lfernandes.org, tglx@...utronix.de, swood@...hat.com,
        williams@...hat.com, juri.lelli@...hat.com,
        linux-rt-users@...r.kernel.org, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org, mingo@...nel.org
Subject: Re: RCU use of swait

On 2020-03-04 16:35:26 [-0800], Paul E. McKenney wrote:
> Hello!
Hi Paul,

> Or is there some other reason why {S,}RCU needs to use swait that I
> am forgetting?

swait can be used in hardirq-context (on RT) that is in a section within
local_irq_save() / raw_spin_lock() and so.
wait on the hand uses spinlock_t which can not be used in this context.
So if you have no users which fall into that category then you could
move back to wait.h.

> 							Thanx, Paul
Sebastian