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