linux-kernel - Re: [PATCH v3 2/2] mcb: use short version for function pointer for mcb_free

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Message-ID: <352fb63a17943b974f5bf6eebb4d861ae8307b24.camel@duagon.com>
Date:   Fri, 22 Sep 2023 12:28:14 +0000
From:   Rodríguez Barbarin, José Javier 
        <josejavier.rodriguez@...gon.com>
To:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC:     "jirislaby@...nel.org" <jirislaby@...nel.org>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "jth@...nel.org" <jth@...nel.org>,
        Sanjuán García, Jorge 
        <Jorge.SanjuanGarcia@...gon.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "morbidrsa@...il.com" <morbidrsa@...il.com>
Subject: Re: [PATCH v3 2/2] mcb: use short version for function pointer for
 mcb_free_bus

On Wed, 2023-09-20 at 15:18 +0200, gregkh@...uxfoundation.org wrote:
> On Wed, Sep 06, 2023 at 11:49:28AM +0000, Rodríguez Barbarin, José
> Javier wrote:
> > From: Jorge Sanjuan Garcia <jorge.sanjuangarcia@...gon.com>
> > 
> > Just a style change so that the device release callbacks are
> > defined
> > in the same way for devices in mcb_bus and mcb_device.
> > 
> > Signed-off-by: Jorge Sanjuan Garcia
> > <jorge.sanjuangarcia@...gon.com>
> > Co-developed-by: Jose Javier Rodriguez Barbarin
> > <JoseJavier.Rodriguez@...gon.com>
> > Signed-off-by: Jose Javier Rodriguez Barbarin
> > <JoseJavier.Rodriguez@...gon.com>
> > ---
> >  drivers/mcb/mcb-core.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/mcb/mcb-core.c b/drivers/mcb/mcb-core.c
> > index 0cac5bead84f..5c6157b0db75 100644
> > --- a/drivers/mcb/mcb-core.c
> > +++ b/drivers/mcb/mcb-core.c
> > @@ -288,7 +288,7 @@ struct mcb_bus *mcb_alloc_bus(struct device
> > *carrier)
> >         bus->dev.parent = carrier;
> >         bus->dev.bus = &mcb_bus_type;
> >         bus->dev.type = &mcb_carrier_device_type;
> > -       bus->dev.release = &mcb_free_bus;
> > +       bus->dev.release = mcb_free_bus;
> 
> But you aren't fixing the root cause here of an incorrect pointer
> being
> passed to this function, right?
> 
> Yes, removing the single variable is nicer, so the crash doesn't
> happen,
> but you are still passing the wrong pointer around, so why not fix
> that?
> 

> thanks,
> 
> greg k-h

The pointer to struct device in function __mcb_bus_add_devices() always
was the correct one. The problem came when calling to function
to_mcb_device() which was hapenning even for the case of struct device
pointer being a member of struct mcb_bus.

Removing the need for this conversion makes the function generic so
that it will work for both mcb_device and mcb_bus structs. This already
fixes the crash as no member overlapping will occur (is_added in
mcb_device struct and bus_nr in mcb_bus struct).

We belive the pointer is the correct one and this patch series was
actually fixing the root cause of the crash. What do you mean by
"passing the wrong pointer around"? are we missing something?

thanks,