linux-kernel - Re: [PATCH] Bluetooth: hci_core: Use ERR

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Message-ID: <CABBYNZJVv=pJv60P6fYZh65JU+BV5agGfXEh4VenxELEXqtDsA@mail.gmail.com>
Date:   Mon, 18 Jul 2022 16:03:52 -0700
From:   Luiz Augusto von Dentz <luiz.dentz@...il.com>
To:     Khalid Masum <khalid.masum.92@...il.com>
Cc:     Pavel Skripkin <paskripkin@...il.com>,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "linux-bluetooth@...r.kernel.org" <linux-bluetooth@...r.kernel.org>,
        "open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>
Subject: Re: [PATCH] Bluetooth: hci_core: Use ERR_PTR instead of NULL

Hi Khalid,

On Sun, Jul 17, 2022 at 11:34 AM Khalid Masum <khalid.masum.92@...il.com> wrote:
>
> On Sun, Jul 17, 2022 at 10:17 PM Pavel Skripkin <paskripkin@...il.com> wrote:
> >
> > Hi Khalid,
> >
> > Khalid Masum <khalid.masum.92@...il.com> says:
> > > Failure of kzalloc to allocate memory is not reported. Return Error
> > > pointer to ENOMEM if memory allocation fails. This will increase
> > > readability and will make the function easier to use in future.
> > >
> > > Signed-off-by: Khalid Masum <khalid.masum.92@...il.com>
> > > ---
> >
> > [snip]
> >
> > > index a0f99baafd35..ea50767e02bf 100644
> > > --- a/net/bluetooth/hci_core.c
> > > +++ b/net/bluetooth/hci_core.c
> > > @@ -2419,7 +2419,7 @@ struct hci_dev *hci_alloc_dev_priv(int sizeof_priv)
> > >
> > >       hdev = kzalloc(alloc_size, GFP_KERNEL);
> > >       if (!hdev)
> > > -             return NULL;
> > > +             return ERR_PTR(-ENOMEM);
> > >
> >
> > This will break all callers of hci_alloc_dev(). All callers expect NULL
> > in case of an error, so you will leave them with wrong pointer.
>
> You are right. All callers of hci_alloc_dev() need to be able to handle
> the error pointer. I shall send a V2 with all the callers of hci_alloc_dev
> handling the ERR_PTR.
>
> > Also, allocation functionS return an error only in case of ENOMEM, so
> > initial code is fine, IMO
> >

If there just a single error like ENOMEM then Id say this is fine,
just as it is fine for kzalloc.

> I think it makes the memory allocation error handling look to be a bit
> different from what we usually do while allocating memory which is,
> returning an error or an error pointer. Here we are returning a NULL
> without any context, making it a bit unreadable. So I think returning
> an error pointer is better. If I am not mistaken, this also complies with
> the return convention:
> https://www.kernel.org/doc/htmldocs/kernel-hacking/convention-returns.html

Not sure if that would apply to code that is basically a wrapper of kzalloc.

> >
> > Thanks,
> > --Pavel Skripkin
>
>
> Thanks,
>   -- Khalid Masum



-- 
Luiz Augusto von Dentz