Re: [PATCH] Btrfs: Refactor btrfs_lock_cluster() to kill compiler warning

Miao Xie
2014-06-23T10:14:45Z

On Sun, 22 Jun 2014 14:30:09 +0200, Geert Uytterhoeven wrote:
> fs/btrfs/extent-tree.c: In function ‘btrfs_lock_cluster’:
> fs/btrfs/extent-tree.c:6399: warning: ‘used_bg’ may be used uninitialized in this function
>
> - Replace "again: ... goto again;" by standard C "while (1) { ... }",
> - Move block not processed during the first iteration of the loop to the
> end of the loop, which allows to kill the "locked" variable,
>
> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

Looks good to me.

Reviewed-and-Tested-by: Miao Xie <miaox@cn.fujitsu.com>

> ---
> Please review, compile tested only.
> ---
> fs/btrfs/extent-tree.c | 42 ++++++++++++++++++++----------------------
> 1 file changed, 20 insertions(+), 22 deletions(-)
>
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 99c253918208..e151c4a73d7b 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -6397,36 +6397,34 @@ btrfs_lock_cluster(struct btrfs_block_group_cache *block_group,
> int delalloc)
> {
> struct btrfs_block_group_cache *used_bg;
> - bool locked = false;
> -again:
> +
> spin_lock(&cluster->refill_lock);
> - if (locked) {
> - if (used_bg == cluster->block_group)
> - return used_bg;
> + while (1) {
> + used_bg = cluster->block_group;
> + if (!used_bg)
> + return NULL;
>
> - up_read(&used_bg->data_rwsem);
> - btrfs_put_block_group(used_bg);
> - }
> + if (used_bg == block_group)
> + return used_bg;
>
> - used_bg = cluster->block_group;
> - if (!used_bg)
> - return NULL;
> + btrfs_get_block_group(used_bg);
>
> - if (used_bg == block_group)
> - return used_bg;
> + if (!delalloc)
> + return used_bg;
>
> - btrfs_get_block_group(used_bg);
> + if (down_read_trylock(&used_bg->data_rwsem))
> + return used_bg;
>
> - if (!delalloc)
> - return used_bg;
> + spin_unlock(&cluster->refill_lock);
> + down_read(&used_bg->data_rwsem);
>
> - if (down_read_trylock(&used_bg->data_rwsem))
> - return used_bg;
> + spin_lock(&cluster->refill_lock);
> + if (used_bg == cluster->block_group)
> + return used_bg;
>
> - spin_unlock(&cluster->refill_lock);
> - down_read(&used_bg->data_rwsem);
> - locked = true;
> - goto again;
> + up_read(&used_bg->data_rwsem);
> + btrfs_put_block_group(used_bg);
> + }
> }
>
> static inline void
>