Date: Tue, 21 Jul 2015 17:54:54 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@amacapital.net>, Jason Baron <jasonbaron0@gmail.com>,
        Mikulas Patocka <mpatocka@redhat.com>,
        Paul Mackerras <paulus@samba.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Vince Weaver <vince@deater.net>, "hillf.zj" <hillf.zj@alibaba-inc.com>,
        Valdis Kletnieks <Valdis.Kletnieks@vt.edu>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Borislav Petkov <bp@alien8.de>, Steven Rostedt <rostedt@goodmis.org>
Subject: Re: Kernel broken on processors without performance counters
Message-ID: <20150721155454.GH18673@twins.programming.kicks-ass.net>
References: <alpine.LRH.2.02.1507081000540.5217@file01.intranet.prod.int.rdu2.redhat.com>
 <20150708160750.GQ19282@twins.programming.kicks-ass.net>
 <CALCETrVqeG=3sKJv=pe9ZfaeRmx9uz+jNmXGmPu-7Hah4NvYDQ@mail.gmail.com>
 <559D8250.8000707@gmail.com>
 <CALCETrUb8tjDLQHF3q=_F7JRXhC8iEHW9o2xFsUbqsmyEOAiCQ@mail.gmail.com>
 <20150710141359.GJ19282@twins.programming.kicks-ass.net>
 <20150721082107.GE18673@twins.programming.kicks-ass.net>
 <alpine.DEB.2.11.1507211726040.18576@nanos>
 <20150721154959.GS19282@twins.programming.kicks-ass.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20150721154959.GS19282@twins.programming.kicks-ass.net>
User-Agent: Mutt/1.5.21 (2012-12-30)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1438
Lines: 41

On Tue, Jul 21, 2015 at 05:49:59PM +0200, Peter Zijlstra wrote:
> On Tue, Jul 21, 2015 at 05:43:27PM +0200, Thomas Gleixner wrote:
> > On Tue, 21 Jul 2015, Peter Zijlstra wrote:
> > 
> > > > -#endif	/* _LINUX_JUMP_LABEL_H */
> > > > +static inline void static_key_enable(struct static_key *key)
> > > > +{
> > > > +	int count = static_key_count(key);
> > > > +
> > > > +	WARN_ON_ONCE(count < 0 || count > 1);
> > > > +
> > > > +	if (!count)
> > > > +		static_key_slow_inc(key);
> > > > +}
> > > > +
> > > > +static inline void static_key_disable(struct static_key *key)
> > > > +{
> > > > +	int count = static_key_count(key);
> > > > +
> > > > +	WARN_ON_ONCE(count < 0 || count > 1);
> > > > +
> > > > +	if (count)
> > > > +		static_key_slow_dec(key);
> > > > +}
> > 
> > The functions above are not part of the interface which should be used
> > in code, right?
> 
> They are in fact. They make it easier to deal with the refcount thing
> when all you want is boolean states.

That is, things like sched_feat_keys[] which is an array of static keys,
the split types doesn't work -- an array can after all have only one
type.

In such cases you do have to be very careful to not wreck things.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/