Btrfs: hash_lock is no longer needed

Before metadata is written to disk, it is updated to reflect that writeout
has begun.  Once this update is done, the block must be cow'd before it
can be modified again.

This update was originally synchronized by using a per-fs spinlock.  Today
the buffers for the metadata blocks are locked before writeout begins,
and everyone that tests the flag has the buffer locked as well.

So, the per-fs spinlock (called hash_lock for no good reason) is no
longer required.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 0 insertions, 4 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 9c3810047976..549271607c17 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1503,7 +1503,6 @@ struct btrfs_root *open_ctree(struct super_block *sb,
         INIT_LIST_HEAD(&fs_info->dead_roots);
         INIT_LIST_HEAD(&fs_info->hashers);
         INIT_LIST_HEAD(&fs_info->delalloc_inodes);
-        spin_lock_init(&fs_info->hash_lock);
         spin_lock_init(&fs_info->delalloc_lock);
         spin_lock_init(&fs_info->new_trans_lock);
         spin_lock_init(&fs_info->ref_cache_lock);
@@ -2361,7 +2360,6 @@ int btrfs_read_buffer(struct extent_buffer *buf, u64 parent_transid)
 int btree_lock_page_hook(struct page *page)
 {
         struct inode *inode = page->mapping->host;
-        struct btrfs_root *root = BTRFS_I(inode)->root;
         struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
         struct extent_buffer *eb;
         unsigned long len;
@@ -2376,9 +2374,7 @@ int btree_lock_page_hook(struct page *page)
                 goto out;
 
         btrfs_tree_lock(eb);
-        spin_lock(&root->fs_info->hash_lock);
         btrfs_set_header_flag(eb, BTRFS_HEADER_FLAG_WRITTEN);
-        spin_unlock(&root->fs_info->hash_lock);
         btrfs_tree_unlock(eb);
         free_extent_buffer(eb);
 out: