When the try lock of the glock failed in prepare_write we were
incorrectly exiting this function with the page still locked.
This was resulting in further I/O to this page hanging.
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
        gfs2_holder_init(ip->i_gl, LM_ST_EXCLUSIVE, GL_ATIME|LM_FLAG_TRY_1CB, &ip->i_gh);
        error = gfs2_glock_nq_atime(&ip->i_gh);
        if (unlikely(error)) {
-               if (error == GLR_TRYFAILED)
+               if (error == GLR_TRYFAILED) {
+                       unlock_page(page);
                        error = AOP_TRUNCATED_PAGE;
+               }
                goto out_uninit;
        }