[PATCH] Btrfs: swap order of two spinlocks (lockdep complains)

[PATCH] Btrfs: swap order of two spinlocks (lockdep complains)

[Stefan Behrens]

may_commit_transaction() calls
        spin_lock(&space_info->lock);
        spin_lock(&delayed_rsv->lock);
and update_global_block_rsv() calls
        spin_lock(&block_rsv->lock);
        spin_lock(&sinfo->lock);

Lockdep complains about this at run time.
Everywhere except in update_global_block_rsv(), the space_info lock is
the outer lock, therefore the locking order in update_global_block_rsv()
is changed.

Signed-off-by: Stefan Behrens <sbehrens@giantdisaster.de>
---
 fs/btrfs/extent-tree.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 84497f8..6fc2e6f 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -4214,8 +4214,8 @@ static void update_global_block_rsv(struct btrfs_fs_info *fs_info)
 
 	num_bytes = calc_global_metadata_size(fs_info);
 
-	spin_lock(&block_rsv->lock);
 	spin_lock(&sinfo->lock);
+	spin_lock(&block_rsv->lock);
 
 	block_rsv->size = num_bytes;
 
@@ -4241,8 +4241,8 @@ static void update_global_block_rsv(struct btrfs_fs_info *fs_info)
 		block_rsv->full = 1;
 	}
 
-	spin_unlock(&sinfo->lock);
 	spin_unlock(&block_rsv->lock);
+	spin_unlock(&sinfo->lock);
 }
 
 static void init_global_block_rsv(struct btrfs_fs_info *fs_info)
-- 
1.7.10

Re: [PATCH] Btrfs: swap order of two spinlocks (lockdep complains)

[Josef Bacik]

On Tue, Apr 24, 2012 at 04:02:09PM +0200, Stefan Behrens wrote:
> may_commit_transaction() calls
>         spin_lock(&space_info->lock);
>         spin_lock(&delayed_rsv->lock);
> and update_global_block_rsv() calls
>         spin_lock(&block_rsv->lock);
>         spin_lock(&sinfo->lock);
> 
> Lockdep complains about this at run time.
> Everywhere except in update_global_block_rsv(), the space_info lock is
> the outer lock, therefore the locking order in update_global_block_rsv()
> is changed.
> 
> Signed-off-by: Stefan Behrens <sbehrens@giantdisaster.de>
> ---
>  fs/btrfs/extent-tree.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 84497f8..6fc2e6f 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -4214,8 +4214,8 @@ static void update_global_block_rsv(struct btrfs_fs_info *fs_info)
>  
>  	num_bytes = calc_global_metadata_size(fs_info);
>  
> -	spin_lock(&block_rsv->lock);
>  	spin_lock(&sinfo->lock);
> +	spin_lock(&block_rsv->lock);
>  
>  	block_rsv->size = num_bytes;
>  
> @@ -4241,8 +4241,8 @@ static void update_global_block_rsv(struct btrfs_fs_info *fs_info)
>  		block_rsv->full = 1;
>  	}
>  
> -	spin_unlock(&sinfo->lock);
>  	spin_unlock(&block_rsv->lock);
> +	spin_unlock(&sinfo->lock);
>  }
>  
>  static void init_global_block_rsv(struct btrfs_fs_info *fs_info)
> -- 
> 1.7.10
> 

Reviewed-by: Josef Bacik <josef@redhat.com>

Thanks,

Josef