On 11/30/2013 09:50 PM, Chen Gang wrote: > On 11/30/2013 08:53 PM, Johannes Berg wrote: >> On Sat, 2013-11-30 at 19:59 +0800, Chen Gang wrote: >>> On 11/29/2013 11:38 PM, Johannes Berg wrote: >>>> >>>>> +++ b/net/mac80211/tx.c >>>>> @@ -1814,8 +1814,9 @@ netdev_tx_t ieee80211_subif_start_xmit(struct >>>>> sk_buff *skb, >>>>> break; >>>>> /* fall through */ >>>>> case NL80211_IFTYPE_AP: >>>>> - if (sdata->vif.type == NL80211_IFTYPE_AP) >>>>> - chanctx_conf = rcu_dereference(sdata->vif.chanctx_conf); >>>>> + if (sdata->vif.type != NL80211_IFTYPE_AP) >>>>> + goto fail_rcu; >>>>> + chanctx_conf = rcu_dereference(sdata->vif.chanctx_conf); >>>> >>>> This change is completely wrong. >>>> >>> >>> Oh, it is. >>> >>> Hmm... for me, this work flow still can be implemented with a little >>> clearer way (at least it will avoid related warning): >>> >>> -------------------------diff begin------------------------------ >>> >>> diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c >>> index c558b24..7076128 100644 >>> --- a/net/mac80211/tx.c >>> +++ b/net/mac80211/tx.c >>> @@ -1810,14 +1810,14 @@ netdev_tx_t ieee80211_subif_start_xmit(struct >>> sk_buff *skb, >>> if (!chanctx_conf) >>> goto fail_rcu; >>> band = chanctx_conf->def.chan->band; >>> - if (sta) >>> - break; >>> - /* fall through */ >>> + if (!sta) >>> + goto try_next; >>> + break; >>> case NL80211_IFTYPE_AP: >>> - if (sdata->vif.type == NL80211_IFTYPE_AP) >>> - chanctx_conf = rcu_dereference(sdata->vif.chanctx_conf); >>> + chanctx_conf = rcu_dereference(sdata->vif.chanctx_conf); >>> if (!chanctx_conf) >>> goto fail_rcu; >>> +try_next: >> >> I don't think that's better than the (fairly obvious) fall-through, and >> has a pretty odd goto. Also, depending on the compiler, it still knows >> the previous case label and doesn't warn. >> > > Yeah, fall-through is obvious. But check 'A' again just near by "case A" > seems a little strange, and some of compilers (or some of versions) are > really not quit smart enough to know it is not a warning. >
Sorry, the paragraph above may lead misunderstanding, I repeated again: - 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. Thanks. > Hmm... for me, if the code (implementation) can express real logical > work flow as much as directly and simply, the code (implementation) is > clear enough (don't mind whether use 'goto' or not). > > > And originally, at first, I am really not quite careful enough, and sent > an incorrect patch after noticed the related compiler's warning. :-) > > > Thanks. > -- Chen Gang -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
