On Fri, Mar 04, 2016 at 02:07:26AM -0500, Valdis.Kletnieks@vt.edu wrote:
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
Thank you, but I don't quite understand. Could you give an example or tell me some books and documnets about this?