Ever since commit 
88b0193d9418 ("perf/callchain: Force USER_DS when
invoking perf_callchain_user()") the caller does this for us.
Signed-off-by: David S. Miller <davem@davemloft.net>
 
 {
        u64 saved_fault_address = current_thread_info()->fault_address;
        u8 saved_fault_code = get_thread_fault_code();
-       mm_segment_t old_fs;
 
        perf_callchain_store(entry, regs->tpc);
 
        if (!current->mm)
                return;
 
-       old_fs = get_fs();
-       set_fs(USER_DS);
-
        flushw_user();
 
        pagefault_disable();
 
        pagefault_enable();
 
-       set_fs(old_fs);
        set_thread_fault_code(saved_fault_code);
        current_thread_info()->fault_address = saved_fault_address;
 }