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Subjectlist-debug variants of rcu list routines.
* Make __list_add_rcu check the next->prev and prev->next pointers
just like __list_add does.
* Make list_del_rcu use __list_del_entry, which does the same checking
at deletion time.

Has been running for a week here without anything being tripped up,
but it seems worth adding for completeness just in case something
ever does corrupt those lists.

Signed-off-by: Dave Jones <davej@redhat.com>

diff -durpN '--exclude-from=/home/davej/.exclude' -u src/git-trees/kernel/linux/include/linux/rculist.h linux-dj/include/linux/rculist.h
--- src/git-trees/kernel/linux/include/linux/rculist.h 2011-07-23 00:05:34.000000000 -0400
+++ linux-dj/include/linux/rculist.h 2012-03-07 00:21:47.050583527 -0500
@@ -30,6 +30,7 @@
* This is only for internal list manipulation where we know
* the prev/next entries already!
*/
+#ifndef CONFIG_DEBUG_LIST
static inline void __list_add_rcu(struct list_head *new,
struct list_head *prev, struct list_head *next)
{
@@ -38,6 +39,10 @@ static inline void __list_add_rcu(struct
rcu_assign_pointer(list_next_rcu(prev), new);
next->prev = new;
}
+#else
+extern void __list_add_rcu(struct list_head *new,
+ struct list_head *prev, struct list_head *next);
+#endif

/**
* list_add_rcu - add a new entry to rcu-protected list
@@ -108,7 +113,7 @@ static inline void list_add_tail_rcu(str
*/
static inline void list_del_rcu(struct list_head *entry)
{
- __list_del(entry->prev, entry->next);
+ __list_del_entry(entry);
entry->prev = LIST_POISON2;
}

diff -durpN '--exclude-from=/home/davej/.exclude' -u src/git-trees/kernel/linux/lib/list_debug.c linux-dj/lib/list_debug.c
--- src/git-trees/kernel/linux/lib/list_debug.c 2011-02-19 12:00:40.000000000 -0500
+++ linux-dj/lib/list_debug.c 2012-03-07 00:18:12.108062540 -0500
@@ -8,6 +8,7 @@

#include <linux/module.h>
#include <linux/list.h>
+#include <linux/rculist.h>

/*
* Insert a new entry between two known consecutive entries.
@@ -73,3 +74,24 @@ void list_del(struct list_head *entry)
entry->prev = LIST_POISON2;
}
EXPORT_SYMBOL(list_del);
+
+/*
+ * RCU variants.
+ */
+void __list_add_rcu(struct list_head *new,
+ struct list_head *prev, struct list_head *next)
+{
+ WARN(next->prev != prev,
+ "list_add_rcu corruption. next->prev should be "
+ "prev (%p), but was %p. (next=%p).\n",
+ prev, next->prev, next);
+ WARN(prev->next != next,
+ "list_add_rcu corruption. prev->next should be "
+ "next (%p), but was %p. (prev=%p).\n",
+ next, prev->next, prev);
+ new->next = next;
+ new->prev = prev;
+ rcu_assign_pointer(list_next_rcu(prev), new);
+ next->prev = new;
+}
+EXPORT_SYMBOL(__list_add_rcu);


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