linux-kernel - Re: [patch 1/2] Linux Kernel Markers

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Message-ID: <20071204194506.GA1431@Krystal>
Date:	Tue, 4 Dec 2007 14:45:06 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, hch@...radead.org, mmlnx@...ibm.com,
	dipankar@...ibm.com, dsmith@...hat.com, paulmck@...ibm.com
Subject: Re: [patch 1/2] Linux Kernel Markers - Support Multiple Probes

* Andrew Morton (akpm@...ux-foundation.org) wrote:
> On Tue, 4 Dec 2007 14:21:00 -0500
> Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> wrote:
> 
> > > > + */
> > > > +void marker_probe_cb(const struct marker *mdata, void *call_private,
> > > > +	const char *fmt, ...)
> > > > +{
> > > > +	va_list args;
> > > > +	char ptype;
> > > > +
> > > > +	preempt_disable();
> > > 
> > > What are the preempt_disable()s doing in here?
> > > 
> > > Unless I missed something obvious, a comment is needed here (at least).
> > > 
> > 
> > They make sure the teardown of the callbacks can be done correctly when
> > they are in modules and they insure RCU read coherency. Will add
> > comment.
> 
> So shouldn't it be using rcu_read_lock()?  If that does not suit, should we
> be adding new rcu primitives rather than open-coding and adding dependencies?

Hrm, yes, good point. Since there seems to be extra magic under
__acquire(RCU);  and  rcu_read_acquire();, the the fact that I use
rcu_barrier() for synchronization, we should. I'll change it.


-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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