The patch titled
list.h: add debug version of list_empty
has been added to the -mm tree. Its filename is
listh-add-debug-version-of-list_empty.patch
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------------------------------------------------------
Subject: list.h: add debug version of list_empty
From: Phil Carmody <ext-phil.2.carmody@xxxxxxxxx>
Heed the notice in list_del: "Note: list_empty() on entry does not return
true after this, the entry is in an undefined state.", and check for
precisely that condition.
There are currently a few instances in the code of this sequence:
if(!list_empty(pnode))
list_del(pnode);
which seems to be useless or dangerous if intended to protect from
repeated del's. And given that I've seen an oops pointing to a
dereference of poison in such a list_empty, I'm veering towards dangerous.
This patch would make such errors obvious.
Nothing is changed in the non-DEBUG_LIST build.
Signed-off-by: Phil Carmody <ext-phil.2.carmody@xxxxxxxxx>
Cc: Paul Menage <menage@xxxxxxxxxx>
Cc: Li Zefan <lizf@xxxxxxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx>
Cc: Andi Kleen <andi@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/list.h | 4 ++++
lib/list_debug.c | 18 ++++++++++++++++++
2 files changed, 22 insertions(+)
diff -puN include/linux/list.h~listh-add-debug-version-of-list_empty include/linux/list.h
--- a/include/linux/list.h~listh-add-debug-version-of-list_empty
+++ a/include/linux/list.h
@@ -183,10 +183,14 @@ static inline int list_is_last(const str
* list_empty - tests whether a list is empty
* @head: the list to test.
*/
+#ifndef CONFIG_DEBUG_LIST
static inline int list_empty(const struct list_head *head)
{
return head->next == head;
}
+#else
+extern int list_empty(const struct list_head *head);
+#endif
/**
* list_empty_careful - tests whether a list is empty and not being modified
diff -puN lib/list_debug.c~listh-add-debug-version-of-list_empty lib/list_debug.c
--- a/lib/list_debug.c~listh-add-debug-version-of-list_empty
+++ a/lib/list_debug.c
@@ -73,3 +73,21 @@ void list_del(struct list_head *entry)
entry->prev = LIST_POISON2;
}
EXPORT_SYMBOL(list_del);
+
+/**
+ * list_empty - tests whether a list is empty
+ * @head: the list to test.
+ */
+int list_empty(const struct list_head *head)
+{
+ if ((head->prev == LIST_POISON2) || (head->prev == LIST_POISON1))
+ WARN(1, "list_empty performed on a node "
+ "at %p removed from a list.\n", head);
+ else
+ WARN((head->prev == head) != (head->next == head),
+ "list_empty corruption. %p<-%p->%p is half-empty.\n",
+ head->prev, head, head->next);
+
+ return head->next == head;
+}
+EXPORT_SYMBOL(list_empty);
_
Patches currently in -mm which might be from ext-phil.2.carmody@xxxxxxxxx are
cgroups-if-you-list_empty-a-head-then-dont-list_del-it.patch
linux-next.patch
calibrate-extract-fall-back-calculation-into-own-helper.patch
calibrate-home-in-on-correct-lpj-value-more-quickly.patch
calibrate-retry-with-wider-bounds-when-converge-seems-to-fail.patch
calibrate-retry-with-wider-bounds-when-converge-seems-to-fail-fix.patch
listh-add-debug-version-of-list_empty.patch
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