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From:   Alex Dewar <alex.dewar90@gmail.com>
Date:   Sat, 7 Nov 2020 13:49:08 +0000
To:     Kalle Valo <kvalo@codeaurora.org>
Cc:     Alex Dewar <alex.dewar90@gmail.com>, netdev@vger.kernel.org,
        Carl Huang <cjhuang@codeaurora.org>,
        linux-wireless@vger.kernel.org, linux-kernel@vger.kernel.org,
        "David S. Miller" <davem@davemloft.net>,
        ath11k@lists.infradead.org, Jakub Kicinski <kuba@kernel.org>
Subject: Re: [PATCH 2/2] ath11k: Handle errors if peer creation fails
Message-ID: <20201107134908.ncne6nm7yyibp3qt@medion>
References: <20201004100218.311653-1-alex.dewar90@gmail.com>
 <87blhfbysb.fsf@codeaurora.org>
 <20201006081321.e2tf5xrdhnk4j3nq@medion>
 <87pn4pfm19.fsf@codeaurora.org>
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On Sat, Nov 07, 2020 at 01:23:30PM +0200, Kalle Valo wrote:
> Alex Dewar <alex.dewar90@gmail.com> writes:
> 
> > On Tue, Oct 06, 2020 at 10:26:28AM +0300, Kalle Valo wrote:
> >> Alex Dewar <alex.dewar90@gmail.com> writes:
> >> 
> >> > ath11k_peer_create() is called without its return value being checked,
> >> > meaning errors will be unhandled. Add missing check and, as the mutex is
> >> > unconditionally unlocked on leaving this function, simplify the exit
> >> > path.
> >> >
> >> > Addresses-Coverity-ID: 1497531 ("Code maintainability issues")
> >> > Fixes: 701e48a43e15 ("ath11k: add packet log support for QCA6390")
> >> > Signed-off-by: Alex Dewar <alex.dewar90@gmail.com>
> >> > ---
> >> >  drivers/net/wireless/ath/ath11k/mac.c | 21 +++++++++------------
> >> >  1 file changed, 9 insertions(+), 12 deletions(-)
> >> >
> >> > diff --git a/drivers/net/wireless/ath/ath11k/mac.c b/drivers/net/wireless/ath/ath11k/mac.c
> >> > index 7f8dd47d2333..58db1b57b941 100644
> >> > --- a/drivers/net/wireless/ath/ath11k/mac.c
> >> > +++ b/drivers/net/wireless/ath/ath11k/mac.c
> >> > @@ -5211,7 +5211,7 @@ ath11k_mac_op_assign_vif_chanctx(struct ieee80211_hw *hw,
> >> >  	struct ath11k *ar = hw->priv;
> >> >  	struct ath11k_base *ab = ar->ab;
> >> >  	struct ath11k_vif *arvif = (void *)vif->drv_priv;
> >> > -	int ret;
> >> > +	int ret = 0;
> >> 
> >> I prefer not to initialise the ret variable.
> >> 
> >> >  	arvif->is_started = true;
> >> >  
> >> >  	/* TODO: Setup ps and cts/rts protection */
> >> >  
> >> > -	mutex_unlock(&ar->conf_mutex);
> >> > -
> >> > -	return 0;
> >> > -
> >> > -err:
> >> > +unlock:
> >> >  	mutex_unlock(&ar->conf_mutex);
> >> >  
> >> >  	return ret;
> >> 
> >> So in the pending branch I changed this to:
> >> 
> >> 	ret = 0;
> >> 
> >> out:
> >> 	mutex_unlock(&ar->conf_mutex);
> >> 
> >> 	return ret;
> >> 
> >> Please check.
> >
> > I'm afraid you've introduced a bug ;). The body of the first if-statement
> > in the function doesn't set ret because no error has occurred. So now
> > it'll jump to the label and the function will return ret uninitialized.
> 
> Ouch, so I did. Good catch! I would have hoped that GCC warns about that
> but it didn't.
> 
> I fixed the bug and added also a warning messages if peer_create()
> fails:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/kvalo/ath.git/commit/?h=pending&id=e3e7b8072fa6bb0928b9066cf76e19e6bd2ec663
> 
> Does this look better now? :)

LGTM!

> 
> > With the gcc extension, ret will be initialised to zero anyway, so we're
> > not saving anything by explicitly assigning to ret later in the
> > function.
> 
> I prefer not to initialise ret in the beginning of the function and I
> try to maintain that style in ath11k. I think it's more readable that
> the error value is assigned just before the goto.

Fair enough. I appreciate that it's a style issue.

> 
> -- 
> https://patchwork.kernel.org/project/linux-wireless/list/
> 
> https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches