From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753912AbcGUTwI (ORCPT ); Thu, 21 Jul 2016 15:52:08 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43834 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752077AbcGUTwF (ORCPT ); Thu, 21 Jul 2016 15:52:05 -0400 Subject: Re: __rtc_read_alarm missing month/year field bug? To: joe.lawrence@redhat.com, "linux-kernel@vger.kernel.org" , rtc-linux@googlegroups.com References: <5768148E.8090304@stratus.com> <57716404.9080204@stratus.com> Cc: Alexandre Belloni , Alessandro Zummo From: Joe Lawrence X-Enigmail-Draft-Status: N1110 Organization: Red Hat Message-ID: <579127E2.9040706@redhat.com> Date: Thu, 21 Jul 2016 15:52:02 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.8.0 MIME-Version: 1.0 In-Reply-To: <57716404.9080204@stratus.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Thu, 21 Jul 2016 19:52:05 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/19/2016, Alexandre Belloni wrote: > > Well like said in my previous mail, I don't think the rollover is the > issue here but I'm interested in knowing what conditions are leading > to endless interrupts. Hi Alexandre, Unfortunately I've switched employers so I no longer have access to the hardware, but if I remember correctly the scenario went like this: - boot machine with RTC alarm set in far future - run 'hwclock' user program - hwclock sync to clock tick - RTC_UIE_ON - RTC_UIE_OFF - kernel sees RTC alarm is outstanding - hpet_rtc_interrupt's start streaming in In the case of this hardware platform, there was a problem with the CMOS RTC read such that hpet_rtc_interrupt / rtc_cmos_read believed that the RTC was busy updating ... that code would delay long enough that the next HPET rtc interrupt would come in right behind it and choke the CPU from scheduling anything else. That platform-specific bug aside, I thought I would report this strangeness in case it was a real bug -- looks like I didn't fully consider the rollover case. -- Joe