Messages in this thread | | | Date | Sun, 29 Sep 2002 10:27:31 -0400 | From | Zach Brown <> | Subject | Re: [PATCH] 2.5.39 list_head debugging |
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> > This patch adds some straight-forward assertions that check the > > validity of arguments to the list_* inlines. [...] > > + BUG_ON(list == NULL); > + BUG_ON(list->next == NULL); > + BUG_ON(list->prev == NULL); > > these checks are not needed - they'll trivially be oopsing when trying to > use them, right?
sure, it's just nice to get the message immediately.
> + BUG_ON((list->next == list) && (list->prev != list)); > + BUG_ON((list->prev == list) && (list->next != list)); > > arent these redundant? If list->next->prev == list and list->prev->next == > list, then if list->next == list then list->prev == list. Ditto for the > other rule.
I don't think so. these check for the very strange list state that results from double list_adds. its an accident of the ordering of our member assignments that result in a pretty strange looking list state after a double_add. it passes all the double-linked assertions (list->{next,prev}->{prev,next} == list) but doesn't follow the rule that both prev and next must point to list if either of them do.
> so i think we only need the following two checks: > > + BUG_ON(list->next->prev != list); > + BUG_ON(list->prev->next != list);
try a double list_add(). these will pass, but the list is not a happy camper :)
> and we could as well add these unconditionally (no .config complexity > needed), until 2.6.0 or so, hm?
I'd love that. It was just a bit of sugar to help the medicine go down.
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