[2/2] btrfs: print-tree: Add locking status output for debug build

Commit Message

Qu Wenruo April 11, 2018, 9:08 a.m. UTC

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

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

Signed-off-by: Qu Wenruo <[e-mail]>
---
 fs/btrfs/print-tree.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

Comments

David Sterba April 19, 2018, 1:01 p.m. UTC | #1

On Wed, Apr 11, 2018 at 05:08:13PM +0800, Qu Wenruo wrote:
> It's pretty handy if we can get debug output for locking status of an
> extent buffer, specially for race related debugging.
> 
> So add the following output for btrfs_print_tree() and
> btrfs_print_leaf():
> - refs
> - write_locks (as w:%u)
> - read_locks (as r:%u)
> - blocking_writers (as bw:%u)
> - blocking_readers (as br:%u)
> - spinning_writers (as sw:%u)
> - spinning_readers (as sr:%u)
> - lock_owner
> - current->pid

Useful, but atomic is 'int' (%d), and pid_t is also int in disguise
(maybe there's a special printk specifier for that).
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Patch

diff --git a/fs/btrfs/print-tree.c b/fs/btrfs/print-tree.c
index 9904cf741e1c..7f0ada51e5fe 100644
--- a/fs/btrfs/print-tree.c
+++ b/fs/btrfs/print-tree.c
@@ -179,6 +179,26 @@  static void print_uuid_item(struct extent_buffer *l, unsigned long offset,
 	}
 }
 
+/*
+ * Helper to output refs and locking status.
+ *
+ * Useful to debug race related problem
+ */
+static void print_eb_refs_lock(struct extent_buffer *eb)
+{
+#ifdef CONFIG_BTRFS_DEBUG
+	btrfs_info(eb->fs_info,
+"refs %u lock(w:%u r:%u bw:%u br:%u sw:%u sr:%u) 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;
@@ -206,6 +226,7 @@  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);
@@ -360,6 +381,7 @@  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",