Btrfs: avoid taking the trans_mutex in btrfs_end_transaction

I've been working on making our O_DIRECT latency not suck and I noticed we were
taking the trans_mutex in btrfs_end_transaction.  So to do this we convert
num_writers and use_count to atomic_t's and just decrement them in
btrfs_end_transaction.  Instead of deleting the transaction from the trans list
in put_transaction we do that in btrfs_commit_transaction() since that's the
only time it actually needs to be removed from the list.  Thanks,

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

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index a272bfd74ea0..ef6865c17cd6 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3136,7 +3136,7 @@ static int btrfs_cleanup_transaction(struct btrfs_root *root)
                 btrfs_destroy_pinned_extent(root,
                                             root->fs_info->pinned_extents);
 
-                t->use_count = 0;
+                atomic_set(&t->use_count, 0);
                 list_del_init(&t->list);
                 memset(t, 0, sizeof(*t));
                 kmem_cache_free(btrfs_transaction_cachep, t);