> On Fri, Mar 12, 2010 at 11:39:25PM +0100, Florian Mickler wrote:
> > On Fri, 12 Mar 2010 13:20:26 -0800
> > Dmitry Torokhov <dmitry.torokhov@gmail.com> wrote:
> >
> > > On Fri, Mar 12, 2010 at 09:57:43PM +0100, Florian Mickler wrote:
> > > > On Fri, 12 Mar 2010 10:22:09 -0800
> > > > Dmitry Torokhov <dmitry.torokhov@gmail.com> wrote:
> > > >
> > > > > On Fri, Mar 12, 2010 at 07:03:08PM +0100,
florian@mickler.org wrote:
> > > > > >
> > > > > > +static ssize_t rfkill_hard_show(struct device *dev,
> > > > > > + struct device_attribute *attr,
> > > > > > + char *buf)
> > > > > > +{
> > > > > > + struct rfkill *rfkill = to_rfkill(dev);
> > > > > > + unsigned long flags;
> > > > > > + u32 state;
> > > > > > +
> > > > > > + spin_lock_irqsave(&rfkill->lock, flags);
> > > > > > + state = rfkill->state;
> > > > > > + spin_unlock_irqrestore(&rfkill->lock, flags);
> > > > >
> > > > > Why exactly is this lock needed?
> > > >
> > > > The rfkill state is updated from multiple contexts... Am I overlooking
> > > > smth obvious here?
> > > >
> > >
> > > You are not updating but reading... Are you concerned about seeing
> > > a partial write to u32? It does not happen.
> > >
> > Hm.. You shure? On every arch that supports wireless drivers?
> >
> > I've just copied that code from the old sysfs state-file handler.
> > So I assumed that reading partial updated state can happen... Also I
> > just searched a little but did not find anything, cause i didn't know
> > where to look. Who garantees this? Is it a gcc thing?
> >
>
> None of the arches would do byte-by-byte writes to a u32, they'd write
> dword at once. Also, even if they could, you are interested in a single
> flag (bit). You do realize that once you leave spinlock whatever you
> fetched is stale data and may not be trusted?
