linux-kernel - Re: [PATCH RFC 0/5] Remove some notrace RCU APIs

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Message-ID: <20190525141954.GA176647@google.com>
Date:   Sat, 25 May 2019 10:19:54 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Ingo Molnar <mingo@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Josh Triplett <josh@...htriplett.org>, kvm-ppc@...r.kernel.org,
        Lai Jiangshan <jiangshanlai@...il.com>,
        linux-doc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>,
        Paul Mackerras <paulus@...abs.org>, rcu@...r.kernel.org
Subject: Re: [PATCH RFC 0/5] Remove some notrace RCU APIs

On Sat, May 25, 2019 at 07:08:26AM -0400, Steven Rostedt wrote:
> On Sat, 25 May 2019 04:14:44 -0400
> Joel Fernandes <joel@...lfernandes.org> wrote:
> 
> > > I guess the difference between the _raw_notrace and just _raw variants
> > > is that _notrace ones do a rcu_check_sparse(). Don't we want to keep
> > > that check?  
> > 
> > This is true.
> > 
> > Since the users of _raw_notrace are very few, is it worth keeping this API
> > just for sparse checking? The API naming is also confusing. I was expecting
> > _raw_notrace to do fewer checks than _raw, instead of more. Honestly, I just
> > want to nuke _raw_notrace as done in this series and later we can introduce a
> > sparse checking version of _raw if need-be. The other option could be to
> > always do sparse checking for _raw however that used to be the case and got
> > changed in http://lists.infradead.org/pipermail/linux-afs/2016-July/001016.html
> 
> What if we just rename _raw to _raw_nocheck, and _raw_notrace to _raw ?

That would also mean changing 160 usages of _raw to _raw_nocheck in the
kernel :-/.

The tracing usage of _raw_notrace is only like 2 or 3 users. Can we just call
rcu_check_sparse directly in the calling code for those and eliminate the APIs?

I wonder what Paul thinks about the matter as well.

thanks, Steven!