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

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Message-ID: <20190525081444.GC197789@google.com>
Date:   Sat, 25 May 2019 04:14:44 -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 Fri, May 24, 2019 at 11:24:58PM -0400, Steven Rostedt wrote:
> On Fri, 24 May 2019 19:49:28 -0400
> "Joel Fernandes (Google)" <joel@...lfernandes.org> wrote:
> 
> > The series removes users of the following APIs, and the APIs themselves, since
> > the regular non - _notrace variants don't do any tracing anyway.
> >  * hlist_for_each_entry_rcu_notrace
> >  * rcu_dereference_raw_notrace
> > 
> 
> 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

thanks a lot,

 - Joel

> 
> -- Steve