On Wed, Dec 04, 2013 at 07:39:07PM +0100, Levente Kurusa wrote: > Date: Wed, 04 Dec 2013 19:39:07 +0100 > From: Levente Kurusa <[email protected]> > To: Borislav Petkov <[email protected]>, Ingo Molnar <[email protected]>, Thomas > Gleixner <[email protected]>, Tony Luck <[email protected]>, "H. Peter > Anvin" <[email protected]>, [email protected], EDAC <[email protected]>, > LKML <[email protected]> > Subject: Re: [PATCH] x86: mcheck: call put_device on device_register failure > User-Agent: Mozilla/5.0 (X11; Linux i686; rv:24.0) Gecko/20100101 > Thunderbird/24.1.0 > > 2013-12-04 08:38, Chen, Gong: > > On Tue, Dec 03, 2013 at 06:01:50PM +0100, Borislav Petkov wrote: > >> Date: Tue, 3 Dec 2013 18:01:50 +0100 > >> From: Borislav Petkov <[email protected]> > >> To: "Chen, Gong" <[email protected]> > >> Cc: Levente Kurusa <[email protected]>, Ingo Molnar <[email protected]>, > >> Thomas Gleixner <[email protected]>, Tony Luck <[email protected]>, "H. > >> Peter Anvin" <[email protected]>, [email protected], EDAC > >> <[email protected]>, LKML <[email protected]> > >> Subject: Re: [PATCH] x86: mcheck: call put_device on device_register > >> failure > >> User-Agent: Mutt/1.5.21 (2010-09-15) > >> > >> Can you please fix your > >> > >> Mail-Followup-To: > >> > >> header? It is impossible to reply to your emails without fiddling with > >> the To: and Cc: by hand which gets very annoying over time. > > > > I add some configs in my muttrc. Hope it works. > > > >> > >> On Mon, Dec 02, 2013 at 09:23:30PM -0500, Chen, Gong wrote: > >>> I have some concerns about it. if device_register is failed, it will > >>> backtraces all kinds of conditions automatically, including put_device > >>> definately. So do we really need an extra put_device when it returns > >>> failure? > >> > >> Do you mean the "done:" label in device_add() which does put_device() > >> and which gets called by device_register()? > >> > > > > Not only. I noticed that another put_device under label "Error:". > > > > That label is called when we failed to add the kobject to its parent. > It just puts the parent of the device. I don't think it has anything > to do with us put_device()-ing the actual device too. > OK, you are right. I read some kobject related codes and get:
static inline void kref_init(struct kref *kref)
{
atomic_set(&kref->refcount, 1);
}
The init refcount is 1, which means even if we meet an error and put_device
in device_add, we still need an extra put_device to make refcount = 0
and then release the dev object.
BTW, from the comments of device_register:
"NOTE: _Never_ directly free @dev after calling this function, even
if it returned an error! Always use put_device() to give up the
reference initialized in this function instead. "
Many caller don't follow this logic. For example:
in arch/arm/common/locomo.c
locomo_init_one_child
...
ret = device_register(&dev->dev);
if (ret) {
out:
kfree(dev);
}
...
in arch/parisc/kernel/drivers.c
create_tree_node
...
if (device_register(&dev->dev)) {
kfree(dev);
return NULL;
}
...
etc.
Maybe we need one more patch to fix them all. :-)
> --
> Regards,
> Levente Kurusa
> --
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