Re: [PATCH] cbus-tahvo: Add tahvo_write_reg locking

Michael Büsch
2011-11-07T09:10:19Z

On Mon, 7 Nov 2011 08:10:45 +0200
Felipe Balbi <balbi@ti.com> wrote:

> Hi,
>
> On Sat, Nov 05, 2011 at 05:19:54PM +0100, Michael Büsch wrote:
> > tahvo_write_reg() needs to take the mutex to avoid a race
> > condition with tahvo_set_clear_reg_bits:
> >
> > tahvo_set_clear_reg_bits(): | tahvo_write_reg():
> > __tahvo_read_reg() |
> > | __tahvo_write_reg() <-- race here
> > __tahvo_write_reg() |
> >
> > Signed-off-by: Michael Buesch <m@bues.ch>
> >
> > ---
> >
> > Index: linux-3.1/drivers/cbus/tahvo.c
> > ===================================================================
> > --- linux-3.1.orig/drivers/cbus/tahvo.c 2011-11-05 17:03:39.598846119 +0100
> > +++ linux-3.1/drivers/cbus/tahvo.c 2011-11-05 17:04:36.274768324 +0100
> > @@ -104,7 +104,9 @@ void tahvo_write_reg(struct device *chil
> > {
> > struct tahvo *tahvo = dev_get_drvdata(child->parent);
> >
> > + mutex_lock(&tahvo->mutex);
> > __tahvo_write_reg(tahvo, reg, val);
> > + mutex_unlock(&tahvo->mutex);
>
> yeah, my bad. The same should be done with tahvo_read_reg(). Care to
> resend this patch adding the change to tahvo_read_reg() too...

I think tahvo_read_reg is fine without a lock.
read vs write is already atomic due to the cbus lock.

it's the same situation as for retu. where we also don't need the lock in retu_read_reg.

--
Greetings, Michael.
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