Btrfs devel - Sep 2012 - [PATCH 1/3] btrfs: remove unnecessary -ENOMEM BUG_ON check in extent-tree.c/exclude_super_stripes

The memory allocation failure is BUG_ON in add_excluded_extent (following
the code path) and btrfs_rmap_block. No need to BUG_ON -ENOMEM inside
exclude_super_stripes itself.

Its return value is always 0, and useless for its callers. Set it as void
instead 0-returned.

Signed-off-by: Wang Sheng-Hui <shhuiw@gmail.com>
---
 fs/btrfs/extent-tree.c |   20 +++++++-------------
 1 files changed, 7 insertions(+), 13 deletions(-)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index ba58024..95492cc 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -234,39 +234,33 @@ static void free_excluded_extents(struct btrfs_root *root,
 			  start, end, EXTENT_UPTODATE, GFP_NOFS);
 }
 
-static int exclude_super_stripes(struct btrfs_root *root,
+static void exclude_super_stripes(struct btrfs_root *root,
 				 struct btrfs_block_group_cache *cache)
 {
 	u64 bytenr;
 	u64 *logical;
 	int stripe_len;
-	int i, nr, ret;
+	int i, nr;
 
 	if (cache->key.objectid < BTRFS_SUPER_INFO_OFFSET) {
 		stripe_len = BTRFS_SUPER_INFO_OFFSET - cache->key.objectid;
 		cache->bytes_super += stripe_len;
-		ret = add_excluded_extent(root, cache->key.objectid,
-					  stripe_len);
-		BUG_ON(ret); /* -ENOMEM */
+		add_excluded_extent(root, cache->key.objectid, stripe_len);
 	}
 
 	for (i = 0; i < BTRFS_SUPER_MIRROR_MAX; i++) {
 		bytenr = btrfs_sb_offset(i);
-		ret = btrfs_rmap_block(&root->fs_info->mapping_tree,
-				       cache->key.objectid, bytenr,
-				       0, &logical, &nr, &stripe_len);
-		BUG_ON(ret); /* -ENOMEM */
+		btrfs_rmap_block(&root->fs_info->mapping_tree,
+				 cache->key.objectid, bytenr,
+				 0, &logical, &nr, &stripe_len);
 
 		while (nr--) {
 			cache->bytes_super += stripe_len;
-			ret = add_excluded_extent(root, logical[nr],
-						  stripe_len);
-			BUG_ON(ret); /* -ENOMEM */
+			add_excluded_extent(root, logical[nr], stripe_len);
 		}
 
 		kfree(logical);
 	}
-	return 0;
 }
 
 static struct btrfs_caching_control *
-- 
1.7.1

On Thu, Sep 06, 2012 at 02:40:41PM +0800, Wang Sheng-Hui
wrote:
> The memory allocation failure is BUG_ON in add_excluded_extent (following
> the code path) and btrfs_rmap_block. No need to BUG_ON -ENOMEM inside
> exclude_super_stripes itself.
No please.
> Its return value is always 0, and useless for its callers. Set it as void
> instead 0-returned.
btrfs_rmap_block itself contains a BUG_ON:

3980 int btrfs_rmap_block(struct btrfs_mapping_tree *map_tree,
3981                      u64 chunk_start, u64 physical, u64 devid,
3982                      u64 **logical, int *naddrs, int *stripe_len)
3983 {
3984         struct extent_map_tree *em_tree = &map_tree->map_tree;
3985         struct extent_map *em;
3986         struct map_lookup *map;
3987         u64 *buf;
3988         u64 bytenr;
3989         u64 length;
3990         u64 stripe_nr;
3991         int i, j, nr = 0;
3992
3993         read_lock(&em_tree->lock);
3994         em = lookup_extent_mapping(em_tree, chunk_start, 1);
3995         read_unlock(&em_tree->lock);
3996
3997         BUG_ON(!em || em->start != chunk_start);

And this should be turned into an ''return error'', thus giving
a non-zero return
code that should be handled in the callers.

Eg. this patch attempts to do that
http://www.mail-archive.com/linux-btrfs@vger.kernel.org/msg15470.html

but has not been merged due to incorrect fix inside exclude_super_stripes
(introduced in the patch).

The same objection for return code cleanups will hold for any function that
returns 0 but is full of BUG_ONs.


david

On 2012年09月06日 18:09, David Sterba wrote:
> On Thu, Sep 06, 2012 at 02:40:41PM +0800, Wang Sheng-Hui wrote:
>> The memory allocation failure is BUG_ON in add_excluded_extent
(following
>> the code path) and btrfs_rmap_block. No need to BUG_ON -ENOMEM inside
>> exclude_super_stripes itself.
> 
> No please.
> 
>> Its return value is always 0, and useless for its callers. Set it as
void
>> instead 0-returned.
> 
> btrfs_rmap_block itself contains a BUG_ON:
> 
> 3980 int btrfs_rmap_block(struct btrfs_mapping_tree *map_tree,
> 3981                      u64 chunk_start, u64 physical, u64 devid,
> 3982                      u64 **logical, int *naddrs, int *stripe_len)
> 3983 {
> 3984         struct extent_map_tree *em_tree = &map_tree->map_tree;
> 3985         struct extent_map *em;
> 3986         struct map_lookup *map;
> 3987         u64 *buf;
> 3988         u64 bytenr;
> 3989         u64 length;
> 3990         u64 stripe_nr;
> 3991         int i, j, nr = 0;
> 3992
> 3993         read_lock(&em_tree->lock);
> 3994         em = lookup_extent_mapping(em_tree, chunk_start, 1);
> 3995         read_unlock(&em_tree->lock);
> 3996
> 3997         BUG_ON(!em || em->start != chunk_start);
> 
> And this should be turned into an ''return error'', thus
giving a non-zero return
> code that should be handled in the callers.
> 
> Eg. this patch attempts to do that
> http://www.mail-archive.com/linux-btrfs@vger.kernel.org/msg15470.html
> 
> but has not been merged due to incorrect fix inside exclude_super_stripes
> (introduced in the patch).
> 
> The same objection for return code cleanups will hold for any function that
> returns 0 but is full of BUG_ONs.
> 
> 
> david
Got it. Thanks, David!

Regards,
Sheng-Hui