Re: [PATCH] net: mac80211: tx.c: be sure of 'sdata->vif.type' must be NL80211_IFTYPE_AP when be in NL80211_IFTYPE_AP case

Chen Gang
2013-11-30T23:59:43Z

On 12/01/2013 07:48 AM, Chen Gang wrote:
> On 12/01/2013 04:39 AM, Joe Perches wrote:
>> On Sat, 2013-11-30 at 21:08 +0100, Johannes Berg wrote:
>>> On Sat, 2013-11-30 at 22:02 +0800, Chen Gang wrote:
>>>> - fall-through is obvious (although I did not notice it, originally).
>>>>
>>>> - Check 'A' again just near by "case A" seems a little strange.
>>>>
>>>> - Some compilers aren't quit smart enough to know 'chanctx_conf' is OK.
>>>
>>> I know. If you have any good ideas of how to make it more obvious to the
>>> compiler, I'm all ears, I just don't like any of the solutions offered
>>> so far (and you aren't the first to do so either) :-)
>>>
>
> OK, thanks.
>
>>> FWIW, I find the label to be odd because if you're familiar with the
>>> code then AP/AP_VLAN *should* be identical except for two special things
>>> that are now linearly & neatly handled in the code (the first being the
>>> 4-addr station, the second the chanctx assignment which always has to be
>>> done regardless of 4-addr). IMHO the == check after case should be
>>> enough to make a human reader take a closer look. I understand that you
>>> didn't and that's OK since you were just trying to squelch compile
>>> warnings, but I don't see that this one warrants much attention.
>>
>> The label/test could be moved to save a couple of lines
>> of duplicated code.
>>
>
> Hmm... for me, it must be an implementation which can satisfy all of us.
>
> If ieee80211_subif_start_xmit() is not performance sensitive (I guess
> so), we can use some short static functions instead of some code blocks
> within ieee80211_subif_start_xmit().
>
> - ieee80211_subif_start_xmit() is a long function (600+ lines).
>

Oh, one typo issue (need use 400+ instead of 600+), it is a long
function (although not quite long).

> - use short static function can share some code.
>
> - if code can be shared, the work flow can be more clearer too (don't
> need fall-through or goto).
>
>
> And I guess, the implementation below can cause panic when
> "sdata->vif.type == NL80211_IFTYPE_AP_VLAN". :-(
>
>> Maybe:
>>
>> net/mac80211/tx.c | 14 ++++++--------
>> 1 file changed, 6 insertions(+), 8 deletions(-)
>>
>> diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
>> index 70b5a05..b2160f4 100644
>> --- a/net/mac80211/tx.c
>> +++ b/net/mac80211/tx.c
>> @@ -1777,18 +1777,16 @@ netdev_tx_t ieee80211_subif_start_xmit(struct sk_buff *skb,
>> }
>> ap_sdata = container_of(sdata->bss, struct ieee80211_sub_if_data,
>> u.ap);
>> - chanctx_conf = rcu_dereference(ap_sdata->vif.chanctx_conf);
>> - if (!chanctx_conf)
>> - goto fail_rcu;
>> - band = chanctx_conf->def.chan->band;
>> - if (sta)
>> - break;
>> /* fall through */
>> case NL80211_IFTYPE_AP:
>> - if (sdata->vif.type == NL80211_IFTYPE_AP)
>> - chanctx_conf = rcu_dereference(sdata->vif.chanctx_conf);
>> + chanctx_conf = rcu_dereference(ap_sdata->vif.chanctx_conf);
>> if (!chanctx_conf)
>> goto fail_rcu;
>> + if (sdata->vif.type == NL80211_IFTYPE_AP_VLAN) {
>> + band = chanctx_conf->def.chan->band;
>> + if (sta)
>> + break;
>> + }
>> fc |= cpu_to_le16(IEEE80211_FCTL_FROMDS);
>> /* DA BSSID SA */
>> memcpy(hdr.addr1, skb->data, ETH_ALEN);
>>
>>
>
>

--
Chen Gang