Re: [EXT4 set 2][PATCH 2/5] cleanups: Add extent sanity checks

[Mingming Cao]

On Tue, 2007-07-10 at 16:30 -0700, Andrew Morton wrote:
> On Sun, 01 Jul 2007 03:36:22 -0400
> Mingming Cao <cmm@xxxxxxxxxx> wrote:
> 
> > with the patch all headers are checked. the code should become
> > more resistant to on-disk corruptions. needless BUG_ON() have
> > been removed. please, review for inclusion.
> > 
> > ...
> 
> > @@ -269,6 +239,70 @@
> >  	return size;
> >  }
> >  
> > +static inline int
> > +ext4_ext_max_entries(struct inode *inode, int depth)
> 
> Please remove the `inline'.
> 
done
> `inline' is usually wrong.  It is wrong here.  If this function has a
> single callsite (it has) then the compiler will inline it.  If the function
> later gains more callsites then the compiler will know (correctly) not to
> inline it.
> 
> We hope.  If we find the compiler still inlines a function as large as this
> one then we'd need to use noinline and complain at the gcc developers.
> 
> > +{
> > +	int max;
> > +
> > +	if (depth == ext_depth(inode)) {
> > +		if (depth == 0)
> > +			max = ext4_ext_space_root(inode);
> > +		else
> > +			max = ext4_ext_space_root_idx(inode);
> > +	} else {
> > +		if (depth == 0)
> > +			max = ext4_ext_space_block(inode);
> > +		else
> > +			max = ext4_ext_space_block_idx(inode);
> > +	}
> > +
> > +	return max;
> > +}
> > +
> > +static int __ext4_ext_check_header(const char *function, struct inode *inode,
> > +					struct ext4_extent_header *eh,
> > +					int depth)
> > +{
> > +	const char *error_msg = NULL;
> 
> Unneeded initialisation.
> 
done

> > +	int max = 0;
> > +
> > +	if (unlikely(eh->eh_magic != EXT4_EXT_MAGIC)) {
> > +		error_msg = "invalid magic";
> > +		goto corrupted;
> > +	}
> > +	if (unlikely(le16_to_cpu(eh->eh_depth) != depth)) {
> > +		error_msg = "unexpected eh_depth";
> > +		goto corrupted;
> > +	}
> > +	if (unlikely(eh->eh_max == 0)) {
> > +		error_msg = "invalid eh_max";
> > +		goto corrupted;
> > +	}
> > +	max = ext4_ext_max_entries(inode, depth);
> > +	if (unlikely(le16_to_cpu(eh->eh_max) > max)) {
> > +		error_msg = "too large eh_max";
> > +		goto corrupted;
> > +	}
> > +	if (unlikely(le16_to_cpu(eh->eh_entries) > le16_to_cpu(eh->eh_max))) {
> > +		error_msg = "invalid eh_entries";
> > +		goto corrupted;
> > +	}
> > +	return 0;
> > +
> > +corrupted:
> > +	ext4_error(inode->i_sb, function,
> > +			"bad header in inode #%lu: %s - magic %x, "
> > +			"entries %u, max %u(%u), depth %u(%u)",
> > +			inode->i_ino, error_msg, le16_to_cpu(eh->eh_magic),
> > +			le16_to_cpu(eh->eh_entries), le16_to_cpu(eh->eh_max),
> > +			max, le16_to_cpu(eh->eh_depth), depth);
> > +
> > +	return -EIO;
> > +}
> > +
> >
> > ...
> >
> > +	i = depth = ext_depth(inode);
> >
> 
> Mulitple assignments like this are somewhat unpopular from the coding-style
> POV.  
> 
okay.

> We have a local variable called `i' which is not used as a simple counter
> and which has no explanatory comment.  This is plain bad.  Please find a
> better name for this variable.  Review the code for other such lack of
> clarity - I'm sure there's more.
> 
"i" is is loop counter. I have moved the i= depth to before the while
loop.

> 
> > -	BUG_ON(le16_to_cpu(eh->eh_entries) > le16_to_cpu(eh->eh_max));
> > -	BUG_ON(eh->eh_magic != EXT4_EXT_MAGIC);
> 
> Yeah, this patch improves things a lot.
> 
> How well-tested is it?  Have any of these errors actually been triggered?
> 
> >  			path[i].p_hdr = ext_block_hdr(path[i].p_bh);
> > -			if (ext4_ext_check_header(__FUNCTION__, inode,
> > -							path[i].p_hdr)) {
> > -				err = -EIO;
> > -				goto out;
> > -			}
> >  		}
> >  
> > -		BUG_ON(le16_to_cpu(path[i].p_hdr->eh_entries)
> > -			   > le16_to_cpu(path[i].p_hdr->eh_max));
> > -		BUG_ON(path[i].p_hdr->eh_magic != EXT4_EXT_MAGIC);
> > -
> >  		if (!path[i].p_idx) {
> >  			/* this level hasn't been touched yet */
> >  			path[i].p_idx = EXT_LAST_INDEX(path[i].p_hdr);
> > @@ -1873,17 +1890,24 @@
> >  				i, EXT_FIRST_INDEX(path[i].p_hdr),
> >  				path[i].p_idx);
> >  		if (ext4_ext_more_to_rm(path + i)) {
> > +			struct buffer_head *bh;
> >  			/* go to the next level */
> >  			ext_debug("move to level %d (block %llu)\n",
> >  				  i + 1, idx_pblock(path[i].p_idx));
> >  			memset(path + i + 1, 0, sizeof(*path));
> > -			path[i+1].p_bh =
> > -				sb_bread(sb, idx_pblock(path[i].p_idx));
> > -			if (!path[i+1].p_bh) {
> > +			bh = sb_bread(sb, idx_pblock(path[i].p_idx));
> > +			if (!bh) {
> >  				/* should we reset i_size? */
> >  				err = -EIO;
> >  				break;
> >  			}
> > +			BUG_ON(i + 1 > depth);
> 
> ouch.  Couldn't we do WARN_ON then return -EIO here?

Done
> 
> > +			if (ext4_ext_check_header(inode, ext_block_hdr(bh),
> > +							depth - i - 1)) {
> > +				err = -EIO;
> > +				break;
> > +			}
> > +			path[i+1].p_bh = bh;
> 
> Really that should have been "i + 1".  checkpatch misses this.  It seems to
> be missing more stuff that it used to lately.
Done.

Hi Andrew,
Attached is incremental changes to address your comments. 
Signed-off-by: Mingming Cao <cmm@xxxxxxxxxx>
---
 fs/ext4/extents.c |   14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

Index: linux-2.6.22/fs/ext4/extents.c
===================================================================
--- linux-2.6.22.orig/fs/ext4/extents.c	2007-07-15 23:25:38.000000000 -0700
+++ linux-2.6.22/fs/ext4/extents.c	2007-07-15 23:44:03.000000000 -0700
@@ -239,7 +239,7 @@ static int ext4_ext_space_root_idx(struc
 	return size;
 }
 
-static inline int
+static int
 ext4_ext_max_entries(struct inode *inode, int depth)
 {
 	int max;
@@ -263,7 +263,7 @@ static int __ext4_ext_check_header(const
 					struct ext4_extent_header *eh,
 					int depth)
 {
-	const char *error_msg = NULL;
+	const char *error_msg;
 	int max = 0;
 
 	if (unlikely(eh->eh_magic != EXT4_EXT_MAGIC)) {
@@ -498,7 +498,7 @@ ext4_ext_find_extent(struct inode *inode
 	short int depth, i, ppos = 0, alloc = 0;
 
 	eh = ext_inode_hdr(inode);
-	i = depth = ext_depth(inode);
+	depth = ext_depth(inode);
 	if (ext4_ext_check_header(inode, eh, depth))
 		return ERR_PTR(-EIO);
 
@@ -513,6 +513,7 @@ ext4_ext_find_extent(struct inode *inode
 	}
 	path[0].p_hdr = eh;
 
+	i = depth;
 	/* walk through the tree */
 	while (i) {
 		ext_debug("depth %d: num %d, max %d\n",
@@ -1973,13 +1974,16 @@ int ext4_ext_remove_space(struct inode *
 				err = -EIO;
 				break;
 			}
-			BUG_ON(i + 1 > depth);
+			if (WARN_ON(i + 1 > depth)) {
+				err = -EIO;
+				break;
+			}
 			if (ext4_ext_check_header(inode, ext_block_hdr(bh),
 							depth - i - 1)) {
 				err = -EIO;
 				break;
 			}
-			path[i+1].p_bh = bh;
+			path[i + 1].p_bh = bh;
 
 			/* save actual number of indexes since this
 			 * number is changed at the next iteration */



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