On Fri, 04 Mar 2016 13:02:02 +0800, Navy Cheng said:
> Hi,
>
> When I read the code of list_del(), I find LIST_POISON1 and LIST_POISON2:
>
> static inline void list_del(struct list_head *entry)
> {
> __list_del(entry->prev, entry->next);
> entry->next = LIST_POISON1;
> entry->prev = LIST_POISON2;
> }
>
> Why not set entry->next and entry->prev to NULL ?
To more easily detect different classes of list corruption, use-after-free, and
other programming errors. If ->next and ->prev are NULL, it may be the result
of following a bad pointer. If they're equal to POISON 1 and 2, you're almost
certainly looking at a once-valid pointer that is a use-after-free situation.
It's easy to end up pointing at a zeroed page. The chances of pointing at
some random data that happens to be POISON 1/2 is much lower.
See the code in lib/list_debug.c
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