btrfs: tracepoints: get correct superblock from dentry in event btrfs_sync_file()

If overlay is used on top of btrfs, dentry->d_sb translates to overlay's
super block and fsid assignment will lead to a crash.

Use file_inode(file)->i_sb to always get btrfs_sb.

Reviewed-by: Boris Burkov <[email protected]>
Signed-off-by: Goldwyn Rodrigues <[email protected]>
Signed-off-by: David Sterba <[email protected]>

Author: Goldwyn Rodrigues

include/trace/events/btrfs.h

@@ -769,12 +769,15 @@ TRACE_EVENT(btrfs_sync_file,
 	),
 
 	TP_fast_assign(
-		const struct dentry *dentry = file->f_path.dentry;
-		const struct inode *inode = d_inode(dentry);
+		struct dentry *dentry = file_dentry(file);
+		struct inode *inode = file_inode(file);
+		struct dentry *parent = dget_parent(dentry);
+		struct inode *parent_inode = d_inode(parent);
 
-		TP_fast_assign_fsid(btrfs_sb(file->f_path.dentry->d_sb));
+		dput(parent);
+		TP_fast_assign_fsid(btrfs_sb(inode->i_sb));
 		__entry->ino		= btrfs_ino(BTRFS_I(inode));
-		__entry->parent		= btrfs_ino(BTRFS_I(d_inode(dentry->d_parent)));
+		__entry->parent		= btrfs_ino(BTRFS_I(parent_inode));
 		__entry->datasync	= datasync;
 		__entry->root_objectid	= btrfs_root_id(BTRFS_I(inode)->root);
 	),