linux-ext4 - Re: [PATCH] ext4: no need to remove extent if len is 0 in ext4_es_remove

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Date:	Sat, 23 Feb 2013 12:07:24 +0800
From:	Zheng Liu <gnehzuil.liu@...il.com>
To:	Theodore Ts'o <tytso@....edu>
CC:	Eryu Guan <guaneryu@...il.com>, linux-ext4@...r.kernel.org,
	Zheng Liu <wenqing.lz@...bao.com>
Subject: Re: [PATCH] ext4: no need to remove extent if len is 0 in ext4_es_remove_extent()

Hi Ted,

One minor comment below for the note.

On 02/23/2013 01:55 AM, Theodore Ts'o wrote:
[snip]
> From 7d46e5051453b2c4dfac4e31ae1afb30064cc404 Mon Sep 17 00:00:00 2001
> From: Eryu Guan <guaneryu@...il.com>
> Date: Fri, 22 Feb 2013 12:54:36 -0500
> Subject: [PATCH] ext4: no need to remove extent if len is 0 in
>  ext4_es_remove_extent()
> 
> len is 0 means no extent needs to be removed, so return immediately.
> Otherwise it could trigger the following BUG_ON() in
> ext4_es_remove_extent()
> 
> 	end = lblk + len - 1;
> 	BUG_ON(end < lblk);
> 
> This could be reproduced by a simple truncate(1) command by an
> unprivileged user
> 
> 	truncate -s $(($((2**32 - 1)) * 4096)) /mnt/ext4/testfile
> 
> The same is true for __es_insert_extent().
> 
> Patched kernel passed xfstests regression test.
> 
> Signed-off-by: Eryu Guan <guaneryu@...il.com>
> Signed-off-by: "Theodore Ts'o" <tytso@....edu>
> Reviewed-by: Zheng Liu <wenqing.lz@...bao.com>
> ---
>  fs/ext4/extents_status.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c
> index 9f1380e..2be245b 100644
> --- a/fs/ext4/extents_status.c
> +++ b/fs/ext4/extents_status.c
> @@ -392,6 +392,9 @@ static int __es_insert_extent(struct inode *inode, struct extent_status *newes)
>  	struct rb_node *parent = NULL;
>  	struct extent_status *es;
>  
> +	if (!len)
> +		return 0;
> +

This will cause a compile error because we don't define a 'len'
variable.  But I have noticed that you have fixed it in latest dev
branch.  So just for the note.

Otherwise the patch looks good.
Reviewed-by: Zheng Liu <wenqing.lz@...bao.com>

Thanks for fixing it,
						- Zheng

>  	while (*p) {
>  		parent = *p;
>  		es = rb_entry(parent, struct extent_status, rb_node);
> @@ -456,6 +459,9 @@ int ext4_es_insert_extent(struct inode *inode, ext4_lblk_t lblk,
>  	es_debug("add [%u/%u) %llu %llx to extent status tree of inode %lu\n",
>  		 lblk, len, pblk, status, inode->i_ino);
>  
> +	if (!len)
> +		return 0;
> +
>  	BUG_ON(end < lblk);
>  
>  	newes.es_lblk = lblk;
> @@ -649,6 +655,9 @@ int ext4_es_remove_extent(struct inode *inode, ext4_lblk_t lblk,
>  	es_debug("remove [%u/%u) from extent status tree of inode %lu\n",
>  		 lblk, len, inode->i_ino);
>  
> +	if (!len)
> +		return err;
> +
>  	end = lblk + len - 1;
>  	BUG_ON(end < lblk);
>  
> 

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