btrfs: btrfs_check_shared should manage its own transaction

Commit afce772e87c3 ("btrfs: fix check_shared for fiemap ioctl") added
transaction semantics around calls to btrfs_check_shared() in order to
provide accurate accounting of delayed refs. The transaction management
should be done inside btrfs_check_shared(), so that callers do not need
to manage transactions individually.

Signed-off-by: Edmund Nadolski <enadolski@suse.com>
Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

3 files changed, 23 insertions, 33 deletions

diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index 3725277f6e08..35cfa388dc0b 100644
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -1580,20 +1580,21 @@ int btrfs_find_all_roots(struct btrfs_trans_handle *trans,
 /**
  * btrfs_check_shared - tell us whether an extent is shared
  *
- * @trans: optional trans handle
- *
  * btrfs_check_shared uses the backref walking code but will short
  * circuit as soon as it finds a root or inode that doesn't match the
  * one passed in. This provides a significant performance benefit for
  * callers (such as fiemap) which want to know whether the extent is
  * shared but do not need a ref count.
  *
+ * This attempts to allocate a transaction in order to account for
+ * delayed refs, but continues on even when the alloc fails.
+ *
  * Return: 0 if extent is not shared, 1 if it is shared, < 0 on error.
  */
-int btrfs_check_shared(struct btrfs_trans_handle *trans,
-                       struct btrfs_fs_info *fs_info, u64 root_objectid,
-                       u64 inum, u64 bytenr)
+int btrfs_check_shared(struct btrfs_root *root, u64 inum, u64 bytenr)
 {
+        struct btrfs_fs_info *fs_info = root->fs_info;
+        struct btrfs_trans_handle *trans;
         struct ulist *tmp = NULL;
         struct ulist *roots = NULL;
         struct ulist_iterator uiter;
@@ -1609,14 +1610,18 @@ int btrfs_check_shared(struct btrfs_trans_handle *trans,
                 return -ENOMEM;
         }
 
-        if (trans)
-                btrfs_get_tree_mod_seq(fs_info, &elem);
-        else
+        trans = btrfs_join_transaction(root);
+        if (IS_ERR(trans)) {
+                trans = NULL;
                 down_read(&fs_info->commit_root_sem);
+        } else {
+                btrfs_get_tree_mod_seq(fs_info, &elem);
+        }
+
         ULIST_ITER_INIT(&uiter);
         while (1) {
                 ret = find_parent_nodes(trans, fs_info, bytenr, elem.seq, tmp,
-                                        roots, NULL, root_objectid, inum, 1);
+                                        roots, NULL, root->objectid, inum, 1);
                 if (ret == BACKREF_FOUND_SHARED) {
                         /* this is the only condition under which we return 1 */
                         ret = 1;
@@ -1631,10 +1636,13 @@ int btrfs_check_shared(struct btrfs_trans_handle *trans,
                 bytenr = node->val;
                 cond_resched();
         }
-        if (trans)
+
+        if (trans) {
                 btrfs_put_tree_mod_seq(fs_info, &elem);
-        else
+                btrfs_end_transaction(trans);
+        } else {
                 up_read(&fs_info->commit_root_sem);
+        }
         ulist_free(tmp);
         ulist_free(roots);
         return ret;
diff --git a/fs/btrfs/backref.h b/fs/btrfs/backref.h
index 9c41fbac3009..f9428aaaa77a 100644
--- a/fs/btrfs/backref.h
+++ b/fs/btrfs/backref.h
@@ -68,9 +68,7 @@ int btrfs_find_one_extref(struct btrfs_root *root, u64 inode_objectid,
                           u64 start_off, struct btrfs_path *path,
                           struct btrfs_inode_extref **ret_extref,
                           u64 *found_off);
-int btrfs_check_shared(struct btrfs_trans_handle *trans,
-                       struct btrfs_fs_info *fs_info, u64 root_objectid,
-                       u64 inum, u64 bytenr);
+int btrfs_check_shared(struct btrfs_root *root, u64 inum, u64 bytenr);
 
 int __init btrfs_prelim_ref_init(void);
 void btrfs_prelim_ref_exit(void);
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index d6f761b4fae0..7dd1b2dc7c68 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -20,7 +20,6 @@
 #include "locking.h"
 #include "rcu-string.h"
 #include "backref.h"
-#include "transaction.h"
 
 static struct kmem_cache *extent_state_cache;
 static struct kmem_cache *extent_buffer_cache;
@@ -4606,36 +4605,21 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
                         flags |= (FIEMAP_EXTENT_DELALLOC |
                                   FIEMAP_EXTENT_UNKNOWN);
                 } else if (fieinfo->fi_extents_max) {
-                        struct btrfs_trans_handle *trans;
-
                         u64 bytenr = em->block_start -
                                 (em->start - em->orig_start);
 
                         disko = em->block_start + offset_in_extent;
 
                         /*
-                         * We need a trans handle to get delayed refs
-                         */
-                        trans = btrfs_join_transaction(root);
-                        /*
-                         * It's OK if we can't start a trans we can still check
-                         * from commit_root
-                         */
-                        if (IS_ERR(trans))
-                                trans = NULL;
-
-                        /*
                          * As btrfs supports shared space, this information
                          * can be exported to userspace tools via
                          * flag FIEMAP_EXTENT_SHARED.  If fi_extents_max == 0
                          * then we're just getting a count and we can skip the
                          * lookup stuff.
                          */
-                        ret = btrfs_check_shared(trans, root->fs_info,
-                                        root->objectid,
-                                        btrfs_ino(BTRFS_I(inode)), bytenr);
-                        if (trans)
-                                btrfs_end_transaction(trans);
+                        ret = btrfs_check_shared(root,
+                                                 btrfs_ino(BTRFS_I(inode)),
+                                                 bytenr);
                         if (ret < 0)
                                 goto out_free;
                         if (ret)