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

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Date:	Mon, 11 Feb 2008 14:56:44 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	linux-kernel@...r.kernel.org, andrea@...ranet.com,
	vegard.nossum@...il.com
Subject: Re: [patch] avoid kmemcheck warning in epoll

On Sun, 10 Feb 2008 13:32:01 -0800 (PST)
Davide Libenzi <davidel@...ilserver.org> wrote:

> 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;
> +}

Is epoll the only rbtree-using code which exhibits this problem?  If so,
what is epoll doing differently from all the others?
--
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