Re: 2.6.25-git2: BUG: unable to handle kernel paging request atffffffffffffffff

[Ingo Molnar]

* Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> wrote:

> On Sun, Apr 20, 2008 at 09:59:11PM -0700, Paul E. McKenney wrote:
> > And here is an update with one bug fixed -- testing continues.
> > This is an update of http://lkml.org/lkml/2008/4/20/217, deleting
> > list_for_each_safe_rcu() and fixing hlist_for_each_entry_rcu().
> > Testing continues...
> 
> And it passes.

i have queued up your patch in its form below. (but Linus might beat me 
at applying it)

	Ingo

-------------------->
Subject: RCU, list.h: fix list iterators
From: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
Date: Sun, 20 Apr 2008 21:59:13 -0700

RCU list iterators: should prefetch ever be optimised out with no
side-effects, the current version will lose the barrier completely.

Pointed-out-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
 include/linux/list.h |   48 +++++++++++++++---------------------------------
 1 file changed, 15 insertions(+), 33 deletions(-)
 
Index: linux/include/linux/list.h
===================================================================
--- linux.orig/include/linux/list.h
+++ linux/include/linux/list.h
@@ -631,31 +631,14 @@ static inline void list_splice_init_rcu(
  * as long as the traversal is guarded by rcu_read_lock().
  */
 #define list_for_each_rcu(pos, head) \
-	for (pos = (head)->next; \
-		prefetch(rcu_dereference(pos)->next), pos != (head); \
-        	pos = pos->next)
+	for (pos = rcu_dereference((head)->next); \
+		prefetch(pos->next), pos != (head); \
+        	pos = rcu_dereference(pos->next))
 
 #define __list_for_each_rcu(pos, head) \
-	for (pos = (head)->next; \
-		rcu_dereference(pos) != (head); \
-        	pos = pos->next)
-
-/**
- * list_for_each_safe_rcu
- * @pos:	the &struct list_head to use as a loop cursor.
- * @n:		another &struct list_head to use as temporary storage
- * @head:	the head for your list.
- *
- * Iterate over an rcu-protected list, safe against removal of list entry.
- *
- * This list-traversal primitive may safely run concurrently with
- * the _rcu list-mutation primitives such as list_add_rcu()
- * as long as the traversal is guarded by rcu_read_lock().
- */
-#define list_for_each_safe_rcu(pos, n, head) \
-	for (pos = (head)->next; \
-		n = rcu_dereference(pos)->next, pos != (head); \
-		pos = n)
+	for (pos = rcu_dereference((head)->next); \
+		pos != (head); \
+        	pos = rcu_dereference(pos->next))
 
 /**
  * list_for_each_entry_rcu	-	iterate over rcu list of given type
@@ -668,10 +651,9 @@ static inline void list_splice_init_rcu(
  * as long as the traversal is guarded by rcu_read_lock().
  */
 #define list_for_each_entry_rcu(pos, head, member) \
-	for (pos = list_entry((head)->next, typeof(*pos), member); \
-		prefetch(rcu_dereference(pos)->member.next), \
-			&pos->member != (head); \
-		pos = list_entry(pos->member.next, typeof(*pos), member))
+	for (pos = list_entry(rcu_dereference((head)->next), typeof(*pos), member); \
+		prefetch(pos->member.next), &pos->member != (head); \
+		pos = list_entry(rcu_dereference(pos->member.next), typeof(*pos), member))
 
 
 /**
@@ -686,9 +668,9 @@ static inline void list_splice_init_rcu(
  * as long as the traversal is guarded by rcu_read_lock().
  */
 #define list_for_each_continue_rcu(pos, head) \
-	for ((pos) = (pos)->next; \
-		prefetch(rcu_dereference((pos))->next), (pos) != (head); \
-        	(pos) = (pos)->next)
+	for ((pos) = rcu_dereference((pos)->next); \
+		prefetch((pos)->next), (pos) != (head); \
+        	(pos) = rcu_dereference((pos)->next))
 
 /*
  * Double linked lists with a single pointer list head.
@@ -986,10 +968,10 @@ static inline void hlist_add_after_rcu(s
  * as long as the traversal is guarded by rcu_read_lock().
  */
 #define hlist_for_each_entry_rcu(tpos, pos, head, member)		 \
-	for (pos = (head)->first;					 \
-	     rcu_dereference(pos) && ({ prefetch(pos->next); 1;}) &&	 \
+	for (pos = rcu_dereference((head)->first);			 \
+	        pos && ({ prefetch(pos->next); 1;}) &&			 \
 		({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \
-	     pos = pos->next)
+	     pos = rcu_dereference(pos->next))
 
 #else
 #warning "don't include kernel headers in userspace"
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