btrfs: print-tree: Add eb locking status output for debug build

It's pretty handy if we can get the debug output for locking status of
an extent buffer, specially for race condition related debugging.

So add the following output for btrfs_print_tree() and
btrfs_print_leaf():
- refs
- write_locks (as w:%d)
- read_locks (as r:%d)
- blocking_writers (as bw:%d)
- blocking_readers (as br:%d)
- spinning_writers (as sw:%d)
- spinning_readers (as sr:%d)
- lock_owner
- current->pid

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ update comment ]
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/print-tree.c b/fs/btrfs/print-tree.c
index 21a831d3d087418bc2e4db884f4fd6a25e9df4e5..a4e11cf04671e6777802922d460dec16007b8380 100644 (file)
--- a/fs/btrfs/print-tree.c
+++ b/fs/btrfs/print-tree.c
@@ -166,6 +166,25 @@ static void print_uuid_item(struct extent_buffer *l, unsigned long offset,
        }
 }
 
+/*
+ * Helper to output refs and locking status of extent buffer.  Useful to debug
+ * race condition related problems.
+ */
+static void print_eb_refs_lock(struct extent_buffer *eb)
+{
+#ifdef CONFIG_BTRFS_DEBUG
+       btrfs_info(eb->fs_info,
+"refs %u lock (w:%d r:%d bw:%d br:%d sw:%d sr:%d) lock_owner %u current %u",
+                  atomic_read(&eb->refs), atomic_read(&eb->write_locks),
+                  atomic_read(&eb->read_locks),
+                  atomic_read(&eb->blocking_writers),
+                  atomic_read(&eb->blocking_readers),
+                  atomic_read(&eb->spinning_writers),
+                  atomic_read(&eb->spinning_readers),
+                  eb->lock_owner, current->pid);
+#endif
+}
+
 void btrfs_print_leaf(struct extent_buffer *l)
 {
        struct btrfs_fs_info *fs_info;
@@ -193,6 +212,7 @@ void btrfs_print_leaf(struct extent_buffer *l)
                   "leaf %llu gen %llu total ptrs %d free space %d owner %llu",
                   btrfs_header_bytenr(l), btrfs_header_generation(l), nr,
                   btrfs_leaf_free_space(fs_info, l), btrfs_header_owner(l));
+       print_eb_refs_lock(l);
        for (i = 0 ; i < nr ; i++) {
                item = btrfs_item_nr(i);
                btrfs_item_key_to_cpu(l, &key, i);
@@ -347,6 +367,7 @@ void btrfs_print_tree(struct extent_buffer *c, bool follow)
                   btrfs_header_bytenr(c), level, btrfs_header_generation(c),
                   nr, (u32)BTRFS_NODEPTRS_PER_BLOCK(fs_info) - nr,
                   btrfs_header_owner(c));
+       print_eb_refs_lock(c);
        for (i = 0; i < nr; i++) {
                btrfs_node_key_to_cpu(c, &key, i);
                pr_info("\tkey %d (%llu %u %llu) block %llu gen %llu\n",