[GFS2] Fix ordering of page disposal vs. glock_dq

In case of unlinked files with dirty pages GFS2 wasn't clearing
the pages in quite the right order. This patch clears the pages
earlier (before the qlock_dq) to avoid the situation that the
release of the glock results in attempting to write back data that
has already been deallocated.

This fixes Red Hat bugzilla: #220117

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

fs/gfs2/ops_super.c

@@ -429,6 +429,12 @@ static void gfs2_delete_inode(struct inode *inode)
 	}
 
 	error = gfs2_dinode_dealloc(ip);
+	/*
+	 * Must do this before unlock to avoid trying to write back
+	 * potentially dirty data now that inode no longer exists
+	 * on disk.
+	 */
+	truncate_inode_pages(&inode->i_data, 0);
 
 out_unlock:
 	gfs2_glock_dq(&ip->i_iopen_gh);