linux-kernel - Re: [PATCH 3/3] staging: r8188eu: fix null check in _rtw_free_mlme

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Date:   Mon, 25 Apr 2022 21:48:23 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Vihas Makwana <makvihas@...il.com>
Cc:     Pavel Skripkin <paskripkin@...il.com>,
        Larry Finger <Larry.Finger@...inger.net>,
        Phillip Potter <phil@...lpotter.co.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Michael Straube <straube.linux@...il.com>,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] staging: r8188eu: fix null check in
 _rtw_free_mlme_priv

On Mon, Apr 25, 2022 at 11:25:32PM +0530, Vihas Makwana wrote:
> On Mon, Apr 25, 2022 at 12:30 AM Pavel Skripkin <paskripkin@...il.com> wrote:
> >
> > Hi Vihas,
> >
> > On 4/24/22 19:31, Vihas Makwana wrote:
> > > There's a NULL check on pmlmepriv in rtw_mlme.c:112 which makes no sense
> > > as rtw_free_mlme_priv_ie_data() dereferences it unconditionally and it
> > > would have already crashed at this point.
> > > Fix this by moving rtw_free_mlme_priv_ie_data() inside the check.
> > >
> > > Signed-off-by: Vihas Makwana <makvihas@...il.com>
> >
> > That's good catch, but looks like the check is just redundant
> >
> > This function is called only from it's wrapper called
> > rtw_free_mlme_priv() and rtw_free_mlme_priv() is called from 2 places:
> >
> > 4 drivers/staging/r8188eu/os_dep/os_intfs.c|531 col 2|
> > rtw_free_mlme_priv(&padapter->mlmepriv);
> > 5 drivers/staging/r8188eu/os_dep/os_intfs.c|579 col 2|
> > rtw_free_mlme_priv(&padapter->mlmepriv);
> >
> > _Very_ unlikely that `&padapter->mlmepriv` expression will become NULL.
> >
> So I guess either we should remove the check or mark it with the
> `unlikely()` macro.

The likely/unlikely() macros are only for when you can prove it makes a
difference to benchmark.  They hurt readability, but they're important
for optimizing the fast path.

Just remove the check.

regards,
dan carpenter