Use the magic LIST_POISON* values to detect an incorrect use of list_del on a
deleted entry. This DEBUG_LIST specific warning is easier to understand than
the generic Oops message caused by LIST_POISON dereference.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
---
 lib/list_debug.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/lib/list_debug.c b/lib/list_debug.c
index 1a39f4e..344c710 100644
--- a/lib/list_debug.c
+++ b/lib/list_debug.c
@@ -43,6 +43,12 @@ EXPORT_SYMBOL(__list_add);
  */
 void list_del(struct list_head *entry)
 {
+	WARN(entry->next == LIST_POISON1,
+		"list_del corruption, next is LIST_POISON1 (%p)\n",
+		LIST_POISON1);
+	WARN(entry->next != LIST_POISON1 && entry->prev == LIST_POISON2,
+		"list_del corruption, prev is LIST_POISON2 (%p)\n",
+		LIST_POISON2);
 	WARN(entry->prev->next != entry,
 		"list_del corruption. prev->next should be %p, "
 		"but was %p\n", entry, entry->prev->next);
-- 
1.7.0

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