2014-06-22 12:30:21

by Geert Uytterhoeven

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

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 <[email protected]>
---
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
--
1.9.1

2014-06-23 10:14:45

by Miao Xie

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

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 <[email protected]>

Looks good to me.

Reviewed-and-Tested-by: Miao Xie <[email protected]>

> ---
> 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
>