Re: [PATCH] btrfs: fix a compiler warning of may be used uninitialized

[David Sterba <dsterba@suse.cz>]

On Wed, Sep 02, 2015 at 03:19:59PM +0800, Zhao Lei wrote:
> Not real problem, just avoid warning of:
>  fs/btrfs/inode-map.c: In function 'btrfs_unpin_free_ino':
>  fs/btrfs/inode-map.c:252: warning: 'count' may be used uninitialized in this function
> In gcc 4.8.3
> 
> Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
> ---
>  fs/btrfs/inode-map.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/inode-map.c b/fs/btrfs/inode-map.c
> index d4a582a..e094e3b 100644
> --- a/fs/btrfs/inode-map.c
> +++ b/fs/btrfs/inode-map.c
> @@ -249,7 +249,7 @@ void btrfs_unpin_free_ino(struct btrfs_root *root)
>  	spinlock_t *rbroot_lock = &root->free_ino_pinned->tree_lock;
>  	struct btrfs_free_space *info;
>  	struct rb_node *n;
> -	u64 count;
> +	u64 count = 0;

AFAICS the codepath that would use uninitialized value of count is not
reachable:

		    add_to_ctl = true

270                 if (info->offset > root->ino_cache_progress)
271                         add_to_ctl = false;
272                 else if (info->offset + info->bytes > root->ino_cache_progress)
273                         count = root->ino_cache_progress - info->offset + 1;
274                 else
275                         count = info->bytes;
276
277                 rb_erase(&info->offset_index, rbroot);
278                 spin_unlock(rbroot_lock);
279                 if (add_to_ctl)
280                         __btrfs_add_free_space(ctl, info->offset, count);

count is defined iff add_to_ctl == true, so the patch is not necessary. And I'm
not quite sure that 0 passed down to __btrfs_add_free_space as 'bytes' makes
sense at all.