Date: Fri, 27 Jun 2014 16:43:23 +0200
From: Petr =?iso-8859-1?Q?Ml=E1dek?= <pmladek@suse.cz>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Ingo Molnar <mingo@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Jiri Kosina <jkosina@suse.cz>, Michal Hocko <mhocko@suse.cz>,
        Jan Kara <jack@suse.cz>, Frederic Weisbecker <fweisbec@gmail.com>,
        Dave Anderson <anderson@redhat.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Konstantin Khlebnikov <koct9i@gmail.com>
Subject: Re: [RFC][PATCH 4/5 v2] printk: Add per_cpu printk func to allow
 printk to be diverted
Message-ID: <20140627144323.GG23205@pathway.suse.cz>
References: <20140626214901.596791200@goodmis.org>
 <20140626220130.356038089@goodmis.org>
 <20140627142025.GD23205@pathway.suse.cz>
 <20140627103933.1e7b981b@gandalf.local.home>
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On Fri 2014-06-27 10:39:33, Steven Rostedt wrote:
> On Fri, 27 Jun 2014 16:20:25 +0200
> Petr Ml?dek <pmladek@suse.cz> wrote:
> 
> 
> > >  	va_start(args, fmt);
> > > -	r = vprintk_emit(0, -1, NULL, 0, fmt, args);
> > > +	preempt_disable();
> > 
> > I think that it is too late to disable the preemption here.
> > It has to be done by the printk() caller if it wants to be sure
> > that the requested function is used.
> 
> That's only if the printk() caller cares. But it would be nice that we
> run the printk_func for the CPU that vprintk_func() is on, thus the
> preempt_disable() is required. (in -rt, this would turn into a
> migrate_disable()).

It makes sense. Thanks for explanation.

Best Regards,
Petr
 
> -- Steve
> 
> > 
> > > +	vprintk_func = this_cpu_read(printk_func);
> > > +	r = vprintk_func(fmt, args);
> > > +	preempt_enable();
> > >  	va_end(args);
> > >  
> > >  	return r;
> > 
> > Best Regards,
> > Petr
> 
--
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