btrfs: move extent_buffer::lock_owner to debug section

The lock_owner is used for a rare corruption case and we haven't seen
any reports in years. Move it to the debugging section of eb.  To close
the holes also move log_index so the final layout looks like:

struct extent_buffer {
        u64                        start;                /*     0     8 */
        long unsigned int          len;                  /*     8     8 */
        long unsigned int          bflags;               /*    16     8 */
        struct btrfs_fs_info *     fs_info;              /*    24     8 */
        spinlock_t                 refs_lock;            /*    32     4 */
        atomic_t                   refs;                 /*    36     4 */
        int                        read_mirror;          /*    40     4 */
        s8                         log_index;            /*    44     1 */

        /* XXX 3 bytes hole, try to pack */

        struct callback_head       callback_head __attribute__((__aligned__(8))); /*    48    16 */
        /* --- cacheline 1 boundary (64 bytes) --- */
        struct rw_semaphore        lock;                 /*    64    40 */
        struct page *              pages[16];            /*   104   128 */

        /* size: 232, cachelines: 4, members: 11 */
        /* sum members: 229, holes: 1, sum holes: 3 */
        /* forced alignments: 1, forced holes: 1, sum forced holes: 3 */
        /* last cacheline: 40 bytes */
} __attribute__((__aligned__(8)));

This saves 8 bytes in total and still keeps the lock on a separate cacheline.

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

1 files changed, 23 insertions, 9 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 4e7a929ba1c6..ea043302cc84 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -4803,6 +4803,28 @@ int btrfs_alloc_logged_file_extent(struct btrfs_trans_handle *trans,
 	return ret;
 }
 
+#ifdef CONFIG_BTRFS_DEBUG
+/*
+ * Extra safety check in case the extent tree is corrupted and extent allocator
+ * chooses to use a tree block which is already used and locked.
+ */
+static bool check_eb_lock_owner(const struct extent_buffer *eb)
+{
+	if (eb->lock_owner == current->pid) {
+		btrfs_err_rl(eb->fs_info,
+"tree block %llu owner %llu already locked by pid=%d, extent tree corruption detected",
+			     eb->start, btrfs_header_owner(eb), current->pid);
+		return true;
+	}
+	return false;
+}
+#else
+static bool check_eb_lock_owner(struct extent_buffer *eb)
+{
+	return false;
+}
+#endif
+
 static struct extent_buffer *
 btrfs_init_new_buffer(struct btrfs_trans_handle *trans, struct btrfs_root *root,
 		      u64 bytenr, int level, u64 owner,
@@ -4816,15 +4838,7 @@ btrfs_init_new_buffer(struct btrfs_trans_handle *trans, struct btrfs_root *root,
 	if (IS_ERR(buf))
 		return buf;
 
-	/*
-	 * Extra safety check in case the extent tree is corrupted and extent
-	 * allocator chooses to use a tree block which is already used and
-	 * locked.
-	 */
-	if (buf->lock_owner == current->pid) {
-		btrfs_err_rl(fs_info,
-"tree block %llu owner %llu already locked by pid=%d, extent tree corruption detected",
-			buf->start, btrfs_header_owner(buf), current->pid);
+	if (check_eb_lock_owner(buf)) {
 		free_extent_buffer(buf);
 		return ERR_PTR(-EUCLEAN);
 	}