linux-kernel - [patch] avoid kmemcheck warning in epoll

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Message-ID: <Pine.LNX.4.64.0802101323140.27286@alien.or.mcafeemobile.com>
Date:	Sun, 10 Feb 2008 13:32:01 -0800 (PST)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <andrea@...ranet.com>,
	Vegard Nossum <vegard.nossum@...il.com>
Subject: [patch] avoid kmemcheck warning in epoll

Epoll calls rb_set_parent(n, n) to initialize the rb-tree node, but 
rb_set_parent() accesses node's pointer in its code. This creates a 
warning in kmemcheck (reported by Vegard Nossum) about an uninitialized 
memory access. The warning is harmless since the following rb-tree node 
insert is going to overwrite the node data. In any case I think it's 
better to not have that happening at all, and fix it by properly 
initializing the data.


Signed-off-by: Davide Libenzi <davidel@...ilserver.org>


- Davide


---
 fs/eventpoll.c         |    2 +-
 include/linux/rbtree.h |   12 ++++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

Index: linux-2.6.mod/fs/eventpoll.c
===================================================================
--- linux-2.6.mod.orig/fs/eventpoll.c	2008-02-10 12:36:20.000000000 -0800
+++ linux-2.6.mod/fs/eventpoll.c	2008-02-10 12:50:41.000000000 -0800
@@ -260,7 +260,7 @@
 /* Special initialization for the RB tree node to detect linkage */
 static inline void ep_rb_initnode(struct rb_node *n)
 {
-	rb_set_parent(n, n);
+	rb_init_node(n, n);
 }
 
 /* Removes a node from the RB tree and marks it for a fast is-linked check */
Index: linux-2.6.mod/include/linux/rbtree.h
===================================================================
--- linux-2.6.mod.orig/include/linux/rbtree.h	2008-02-10 12:36:13.000000000 -0800
+++ linux-2.6.mod/include/linux/rbtree.h	2008-02-10 12:51:57.000000000 -0800
@@ -112,6 +112,18 @@
 	struct rb_node *rb_node;
 };
 
+/**
+ * rb_init_node - Initializes the node internal data
+ *
+ * @node: Pointer to the RB-Tree node
+ * @parent: Pointer to the parent node, or NULL
+ *
+ */
+static inline void rb_init_node(struct rb_node *node, struct rb_node *parent)
+{
+	node->rb_parent_color = (unsigned long) parent;
+	node->rb_left = node->rb_right = NULL;
+}
 
 #define rb_parent(r)   ((struct rb_node *)((r)->rb_parent_color & ~3))
 #define rb_color(r)   ((r)->rb_parent_color & 1)
--
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