linux-ext4 - Re: [PATCH] replaced BUG() with return -EIO from ext4_ext_get

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Date:	Fri, 11 Dec 2009 10:07:39 -0800
From:	Frank Mayhar <fmayhar@...gle.com>
To:	Surbhi Palande <surbhi.palande@...onical.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH] replaced BUG() with return -EIO from
	ext4_ext_get_blocks

On Fri, 2009-12-11 at 16:06 +0200, Surbhi Palande wrote:
> This patch fixes the upstream bug# 14286. When the address of an extent
> corresponding to a given block is NULL and the tree is being traversed for
> fetching such an address, a -EIO should be reported instead of a BUG(). This
> situation should normally not occur. However if it does, then the system
> should be rendered usable.
> 
> Signed-off-by: Surbhi Palande <surbhi.palande@...onical.com>
> ---
>  fs/ext4/extents.c |    7 ++++++-
>  1 files changed, 6 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 3a7928f..51f87f3 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -3190,7 +3190,12 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
>  	 * this situation is possible, though, _during_ tree modification;
>  	 * this is why assert can't be put in ext4_ext_find_extent()
>  	 */
> -	BUG_ON(path[depth].p_ext == NULL && depth != 0);
> +	if (path[depth].p_ext == NULL && depth != 0) {
> +		err = -EIO;
> +		printk(KERN_ERR "\n ext4 fs error in %s,%s,%s while reading a block ", \
> +					__FILE__, __func__, __LINE__);
> +		goto out2;
> +	}
>  	eh = path[depth].p_hdr;
>  
>  	ex = path[depth].p_ext;

As it happens, I fixed this locally but, as I considered it a band-aid
fix at the time, I never pushed it to you guys.  My version of the fix
is below; it dumps more information before returning the EIO.  I don't
have a strong preference between the two versions but I would like to
see the commentary included and the extra information is often useful
during debugging.

Signed-off-by:  Frank Mayhar <fmayhar@...gle.com>

 fs/ext4/extents.c |   18 +++++++++++++++++-
 1 files changed, 17 insertions(+), 1 deletions(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index f7bdd55..7aa0bf6 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -2859,8 +2859,24 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
 	 * consistent leaf must not be empty;
 	 * this situation is possible, though, _during_ tree modification;
 	 * this is why assert can't be put in ext4_ext_find_extent()
+	 *
+	 * We don't want to panic in this case, as it can lead to a crash
+	 * loop; instead we want to catch the error and abort.
 	 */
-	BUG_ON(path[depth].p_ext == NULL && depth != 0);
+	if (path[depth].p_ext == NULL && depth != 0) {
+		printk(KERN_ERR
+		       "EXT4-fs (%s): corrupt extent node ino %lu iblock %d"
+		       " depth %d pblock %lld\n",
+		       inode->i_sb->s_id, inode->i_ino, iblock, depth,
+		       path[depth].p_block);
+		if (!path[depth].p_hdr)
+			path[depth].p_hdr = ext_block_hdr(path[depth].p_bh);
+		printk(KERN_ERR "EXT4-fs (%s): eh_entries %d eh_max %d\n",
+		       inode->i_sb->s_id, path[depth].p_hdr->eh_entries,
+		       path[depth].p_hdr->eh_max);
+		err = -EIO;
+		goto out2;
+	}
 	eh = path[depth].p_hdr;
 
 	ex = path[depth].p_ext;
-- 
Frank Mayhar <fmayhar@...gle.com>
Google, Inc.

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