netdev - Re: [PATCH] [RFC] net: dsa: mv88e6xxx: Pre-initialize err in mv88e6xxx_port_bridge

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Date:	Mon, 25 Apr 2016 14:35:14 -0400
From:	Vivien Didelot <vivien.didelot@...oirfairelinux.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	"David S. Miller" <davem@...emloft.net>,
	"netdev\@vger.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] [RFC] net: dsa: mv88e6xxx: Pre-initialize err in mv88e6xxx_port_bridge_join()

Hi Geert,

Geert Uytterhoeven <geert@...ux-m68k.org> writes:

> Hi Vivien,
>
> On Mon, Apr 25, 2016 at 7:31 PM, Vivien Didelot
> <vivien.didelot@...oirfairelinux.com> wrote:
>> Geert Uytterhoeven <geert@...ux-m68k.org> writes:
>>> On Mon, Apr 25, 2016 at 5:03 PM, Vivien Didelot
>>> <vivien.didelot@...oirfairelinux.com> wrote:
>>>> Geert Uytterhoeven <geert@...ux-m68k.org> writes:
>>>>> drivers/net/dsa/mv88e6xxx.c: In function ‘mv88e6xxx_port_bridge_join’:
>>>>> drivers/net/dsa/mv88e6xxx.c:2184: warning: ‘err’ may be used uninitialized in this function
>>>>
>>>> Interesting, I don't have those warnings on 207afda1b5036009...
>>>
>>> It depends on the compiler version (still using 4.1.2) and options.
>>>
>>>>> If netdev_notifier_changeupper_info.upper_dev is ever NULL, the bridge
>>>>> parameter will be NULL too, and the function will return an
>>>>> uninitialized value.
>>>>>
>>>>> Pre-initialize err to zero to fix this.
>>>>>
>>>>> Fixes: 207afda1b5036009 ("net: dsa: mv88e6xxx: share the same default FDB")
>>>>> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
>>>>> ---
>>>>> Can this actually happen?
>>>>
>>>> bridge cannot be NULL here. Also ps->ports[port].bridge_dev is assigned
>>>> to it before entering the for loop, so _mv88e6xxx_port_based_vlan_map
>>>> will be called at least for this port.
>>>
>>> But there's no way the compiler can know that...
>>
>> Or maybe it can in new configurations. Anyway, this fix doesn't hurt,
>> with a relevant commit message, I'd ack it.
>
> What would you consider a relevant commit message?

bridge being NULL is not the reason why err can eventually get returned
uninitialized. The GCC version would be great too, I have no such
warning here with 5.3.0.

Thanks,
-v