Re: [rtc-linux] [PATCH] rtc: recycle id when unloading a rtc driver

[Alexander Holler]

Am 19.12.2012 08:45, schrieb Andrew Morton:
> On Wed, 19 Dec 2012 08:37:07 +0100 Alexander Holler <holler@xxxxxxxxxxxxx> wrote:
>
> > Am 19.12.2012 01:46, schrieb Andrew Morton:
> > > On Thu,  2 Aug 2012 16:53:25 -0700
> > > Vincent Palatin <vpalatin@xxxxxxxxxxxx> wrote:
> > >
> > > > When calling rtc_device_unregister, we are not freeing the id used by the
> > > > driver.
> > > > So when doing a unload/load cycle for a RTC driver (e.g. rmmod rtc_cmos
> > > > && modprobe rtc_cmos), its id is incremented by one. As a consequence,
> > > > we no longer have neither an rtc0 driver nor a /proc/driver/rtc (as it
> > > > only exists for the first driver).
> > > >
> > > > Signed-off-by: Vincent Palatin <vpalatin@xxxxxxxxxxxx>
> > > > ---
> > > >    drivers/rtc/class.c |    1 +
> > > >    1 files changed, 1 insertions(+), 0 deletions(-)
> > > >
> > > > diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c
> > > > index dc4c274..37b1d82 100644
> > > > --- a/drivers/rtc/class.c
> > > > +++ b/drivers/rtc/class.c
> > > > @@ -238,6 +238,7 @@ void rtc_device_unregister(struct rtc_device *rtc)
> > > >    		rtc_proc_del_device(rtc);
> > > >    		device_unregister(&rtc->dev);
> > > >    		rtc->ops = NULL;
> > > > +		ida_simple_remove(&rtc_ida, rtc->id);
> > > >    		mutex_unlock(&rtc->ops_lock);
> > > >    		put_device(&rtc->dev);
> > > >    	}
> > >
> > > Now I think about it, this shouldn't have been needed?
> > >
> > > That put_device() should call rtc_device_release(), which does the
> > > ida_simple_remove().  Isn't that working?
> >
> > It is, see the mini-thread, patch and my comment here:
> >
> > https://lkml.org/lkml/2012/12/6/152
> >
> > Maybe it would be better to move the ida_simple_remove from the
> > rtc_device_release to rt_device_unregister as I've hinted in the above
> > comment. That would make it easier to spot the ida_simple_remove().
>
> I'm all confused.
>
> Lothar's patch simply reverts Vincent's patch.  And that appears to be
> the correct thing to so, as the ida_simple_remove() in
> rtc_device_release() should be sufficient.
>
> But apparently that doesn't work, because Vincent was seeing the RTC
> ID's increment rather than getting reused.
>
> Is it the case that rtc_device_release() is not being called sometimes?
> If so, under what circumstances?

Maybe something (sysfs or whatever) still has a reference to it. Vincent 
should check that.

But I'm sure the ID will be recycled with that put_device() in 
unregister because I've got the same warning as Lothar did when 
(porperly) removing an RTC (with kernel 3.7).

Regards,

Alexander
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