btrfs: switch to refcount_t type for btrfs_trans_handle::use_count

The use_count is a reference counter, we can use the refcount_t type,
though we don't use the atomicity. This is not a performance critical
code and we could catch the underflows. The type is changed from long,
but the number of references will fit an int.

Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index dac688c..6348573 100644 (file)
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -495,8 +495,8 @@ start_transaction(struct btrfs_root *root, unsigned int num_items,
        if (current->journal_info) {
                WARN_ON(type & TRANS_EXTWRITERS);
                h = current->journal_info;
-               h->use_count++;
-               WARN_ON(h->use_count > 2);
+               refcount_inc(&h->use_count);
+               WARN_ON(refcount_read(&h->use_count) > 2);
                h->orig_rsv = h->block_rsv;
                h->block_rsv = NULL;
                goto got_it;
@@ -567,7 +567,7 @@ again:
        h->transid = cur_trans->transid;
        h->transaction = cur_trans;
        h->root = root;
-       h->use_count = 1;
+       refcount_set(&h->use_count, 1);
        h->fs_info = root->fs_info;
 
        h->type = type;
@@ -837,8 +837,8 @@ static int __btrfs_end_transaction(struct btrfs_trans_handle *trans,
        int err = 0;
        int must_run_delayed_refs = 0;
 
-       if (trans->use_count > 1) {
-               trans->use_count--;
+       if (refcount_read(&trans->use_count) > 1) {
+               refcount_dec(&trans->use_count);
                trans->block_rsv = trans->orig_rsv;
                return 0;
        }
@@ -1868,7 +1868,7 @@ static void cleanup_transaction(struct btrfs_trans_handle *trans,
        struct btrfs_transaction *cur_trans = trans->transaction;
        DEFINE_WAIT(wait);
 
-       WARN_ON(trans->use_count > 1);
+       WARN_ON(refcount_read(&trans->use_count) > 1);
 
        btrfs_abort_transaction(trans, err);
 

diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h
index c48a4a0..afa88f0 100644 (file)
--- a/fs/btrfs/transaction.h
+++ b/fs/btrfs/transaction.h
@@ -111,7 +111,7 @@ struct btrfs_trans_handle {
        u64 transid;
        u64 bytes_reserved;
        u64 chunk_bytes_reserved;
-       unsigned long use_count;
+       refcount_t use_count;
        unsigned long delayed_ref_updates;
        struct btrfs_transaction *transaction;
        struct btrfs_block_rsv *block_rsv;