linux-ext4 - Re: [PATCH 1/3] fs/ext4: release kobject/kset even when init/register fail

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Message-ID: <20171128110339.GD83442@rschirone-mbp.local>
Date:   Tue, 28 Nov 2017 12:03:39 +0100
From:   "Riccardo S." <sirmy15@...il.com>
To:     Andreas Dilger <adilger@...ger.ca>
Cc:     Theodore Ts'o <tytso@....edu>,
        linux-ext4 <linux-ext4@...r.kernel.org>,
        gregkh@...uxfoundation.org
Subject: Re: [PATCH 1/3] fs/ext4: release kobject/kset even when
 init/register fail

On 11/27, Andreas Dilger wrote:
> On Nov 27, 2017, at 4:17 PM, Riccardo Schirone <sirmy15@...il.com> wrote:
> > 
> > Even when kobject_init_and_add/kset_register fail, the kobject has been
> > already initialized and the refcount set to 1. Thus it is necessary to
> > release the kobject/kset, to avoid the memory associated with it hanging
> > around forever.
> 
> This seems like a bad programming model.  It doesn't make sense if the
> "init" or "register" function returns an error that you would still have
> to call "put" or "unregister" on the object.  Why not just handle the
> cleanup at the end of "kobject_init_and_add()" or "kobject_register()"
> if there is an error instead of putting the burden on every caller?
> 
> If open() returns an error, I don't need to call close(), and if malloc()
> fails I don't need to call free(), etc.
> 
> Cheers, Andreas
> 

I agree it seems weird at first, but it looks to me the examples you
made involve the *creation* of new objects, so it makes sense that the
function, in case of errors, does not create them at all.

In this case though the kobject_init_and_add is really just a shortcut
for kobject_init + kobject_add and none of these functions create
something for you. It's the caller's job to allocate the necessary
memory, so I think that's the reason why it's still the caller that
calls kobject_put when there's something wrong.

Instead, in kobject_create_and_add, where the creation of the kobject is
inside the function, the kobject is cleaned up if something wrong
happens.

Those are my thoughts anyway.
Regards,

Riccardo