Messages in this thread | | | Date | Sun, 21 Nov 2010 05:55:55 -0500 (EST) | From | "Robert P. J. Day" <> | Subject | should list poisoning only kick in after selecting CONFIG_DEBUG_LIST? |
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a bit confused about list poisoning. there's this from <linux/list.h>:
#ifndef CONFIG_DEBUG_LIST static inline void list_del(struct list_head *entry) { __list_del(entry->prev, entry->next); entry->next = LIST_POISON1; entry->prev = LIST_POISON2; } #else extern void list_del(struct list_head *entry); #endif
which seems a bit weird since, even if you *don't* select CONFIG_DEBUG_LIST, the deleted node's pointers are poisoned. why? that's certainly being done in the debug version of list_del() in lib/list_debug.c, but why is it also being done above? for what purpose?
and if i don't select that debugging option, should *anything* be checking for those poison values?
$ grep -r -A2 LIST_POISON drivers drivers/usb/host/xhci-hub.c: if (cmd->cmd_list.next != LIST_POISON1) drivers/usb/host/xhci-hub.c- list_del(&cmd->cmd_list); drivers/usb/host/xhci-hub.c- spin_unlock_irqrestore(&xhci->lock, flags); -- drivers/usb/host/xhci.c: if (reset_device_cmd->cmd_list.next != LIST_POISON1) drivers/usb/host/xhci.c- list_del(&reset_device_cmd->cmd_list); drivers/usb/host/xhci.c- spin_unlock_irqrestore(&xhci->lock, flags); $
that looks just plain odd. why would normal driver code that is not dependent on CONFIG_DEBUG_LIST be checking for poison values? and if it finds them, why is that not treated as that something has gone significantly wrong, rather than quietly glossing over it?
rday
--
======================================================================== Robert P. J. Day Waterloo, Ontario, CANADA http://crashcourse.ca
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