Btrfs: fix unexpected -EEXIST when creating new inode

The highest objectid, which is assigned to new inode, is decided at
the time of initializing fs roots.  However, in cases where log replay
gets processed, the btree which fs root owns might be changed, so we
have to search it again for the highest objectid, otherwise creating
new inode would end up with -EEXIST.

cc: <stable@vger.kernel.org> v4.4-rc6+
Fixes: f32e48e925 ("Btrfs: Initialize btrfs_root->highest_objectid when loading tree root and subvolume roots")
Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Reviewed-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/tree-log.c

@@ -28,6 +28,7 @@
 #include "hash.h"
 #include "compression.h"
 #include "qgroup.h"
+#include "inode-map.h"
 
 /* magic values for the inode_only field in btrfs_log_inode:
  *
@@ -5685,6 +5686,23 @@ again:
 						      path);
 		}
 
+		if (!ret && wc.stage == LOG_WALK_REPLAY_ALL) {
+			struct btrfs_root *root = wc.replay_dest;
+
+			btrfs_release_path(path);
+
+			/*
+			 * We have just replayed everything, and the highest
+			 * objectid of fs roots probably has changed in case
+			 * some inode_item's got replayed.
+			 *
+			 * root->objectid_mutex is not acquired as log replay
+			 * could only happen during mount.
+			 */
+			ret = btrfs_find_highest_objectid(root,
+						  &root->highest_objectid);
+		}
+
 		key.offset = found_key.offset - 1;
 		wc.replay_dest->log_root = NULL;
 		free_extent_buffer(log->node);