Re: [PATCH] [RFC] i2c: Don't wait for device release in i2c_del_adapter

[Greg Kroah-Hartman <gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org>]

On Thu, Jan 15, 2015 at 06:25:22PM +0200, Pantelis Antoniou wrote:
> Hi Greg,
> 
> > On Jan 14, 2015, at 22:41 , Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:
> > 
> > On Wed, Jan 14, 2015 at 07:24:22PM +0200, Pantelis Antoniou wrote:
> >> I’ll try to dig around tomorrow and see what the real device reference counts
> >> are, but my hunch goes like this:
> >> 
> >> MUX
> >> +—- ADAPTER
> >>    +— DEV.
> >> 
> >> Mux remove method is called, i2c_del_mux_adapter is called on all the channels
> >> of the mux, calling in turn i2c_del_adapter which hangs on completion of the
> >> dev_released.
> >> 
> >> The call to device_unregister never calls the device_type callback (i2c_adapter_dev_release)
> >> because the reference count is not 1 at that point, someone else is having another
> >> reference.
> > 
> 
> First of all, my head hurts. Tracking device references ain’t easy. Is there some kind
> of debugging method you’d recommend for this?

You can turn on debugging for kobjects and the driver core if you want
to slow down your system log a bunch, but it can be helpful for trickier
issues.  Or just sprinkle a few printks around.

> > I don't remember the i2c core code at all, that was a long time ago.
> > 
> 
> Bummer.

Do you remember code you wrote 12 year ago and haven't looked at for at
least 11?  Why expect others to as well? :)

thanks,

greg k-h