linux-kernel - Re: [RFC][PATCH] sched: take rt_rq->rt_runtime_lock around rt_rq->rt

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Message-ID: <alpine.LNX.2.00.1107282313320.20477@swampdragon.chaosbits.net>
Date:	Thu, 28 Jul 2011 23:14:43 +0200 (CEST)
From:	Jesper Juhl <jj@...osbits.net>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>
Subject: Re: [RFC][PATCH] sched: take rt_rq->rt_runtime_lock around
 rt_rq->rt_runtime modification

On Thu, 28 Jul 2011, Peter Zijlstra wrote:

> On Thu, 2011-07-28 at 22:13 +0200, Jesper Juhl wrote:
> > Everywhere (that I could find) where we modify rt_rq->rt_runtime we hold 
> > rt_rq->rt_runtime_lock except in alloc_rt_sched_group(). Shouldn't we do 
> > so - as per this patch. ???
> > 
> > Signed-off-by: Jesper Juhl <jj@...osbits.net>
> > ---
> >  kernel/sched.c |    2 ++
> >  1 files changed, 2 insertions(+), 0 deletions(-)
> > 
> > diff --git a/kernel/sched.c b/kernel/sched.c
> > index ccacdbd..d5a3737 100644
> > --- a/kernel/sched.c
> > +++ b/kernel/sched.c
> > @@ -8488,7 +8488,9 @@ int alloc_rt_sched_group(struct task_group *tg, struct task_group *parent)
> >  			goto err_free_rq;
> >  
> >  		init_rt_rq(rt_rq, cpu_rq(i));
> > +		raw_spin_lock(&rt_rq->rt_runtime_lock);
> >  		rt_rq->rt_runtime = tg->rt_bandwidth.rt_runtime;
> > +		raw_spin_unlock(&rt_rq->rt_runtime_lock);
> >  		init_tg_rt_entry(tg, rt_rq, rt_se, i, parent->rt_se[i]);
> 
> This is init code, the rt_rq is fresh and isn't exposed yet. There isn't
> any concurrency.
> 

I was actually wondering if that was the case, but wasn't sure, so I 
thought - better safe than sorry and ask :-)

Thank you for the feedback.

-- 
Jesper Juhl <jj@...osbits.net>       http://www.chaosbits.net/
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